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                         Sheizaf Rafaeli
                School of Business Administration
                 Hebrew University of Jerusalem
                 Mount Scopus, 91905, Jerusalem
                         Tel. 02-883106
                  Online: [email protected]


                        Robert J. LaRose
                 Department of Telecommunication
                    Michigan State University
                  East Lansing, MI  48824-1212
                        Tel. 517-355-4528

                           March, 1992

Dr. Rafaeli is an Assistant Professor at the School of Business
Administration, the Hebrew University of Jerusalem.  Dr. LaRose
is an Associate Professor at the Department of Telecommunication,
Michigan State University.  The authors wish to acknowledge their
gratitude for support provided by Michigan State University's
Communication Technology Laboratory, the Northern Telecom
University Interaction Program, and the Rekanati Fund.



Collaborative mass media are a new type of mass communications
medium in which the audience acts both as the source and the
receiver of the message.  Theories of discretionary data base
contributions and critical mass theory offer parallel, but in
some ways distinct, explanations for the success of collaborative
media. The present research compared the predictions of these two
perspectives in the context of a national survey of public
electronic bulletin board systems.  The study documented the
nature and extent of electronic bulletin board use and compared
seemingly conflicting predictions about the success of
collaborative media based on the two theoretical perspectives.
File contribution levels and system adoption rates were both
found to be directly related to a measure of symmetry in user
participation.  Content diversity was directly related to
contribution levels, but not to overall adoption levels.  The
results provided limited support for discretionary data base


Collaborative mass media systems, in which the audience is also
the primary source of media content as well as its receiver,
represent a new and significant departure from conventional mass
media forms. They expand the very definition of mass media, from
"one to many" to "many to many" communication. In the past,
audience-generated mass media content has invariably been
subjected to a considerable degree of editorial control and has
generally constituted a relatively small percentage of total
message system content. Contributions came from a such a small
number of audience members that the participants were more
properly regarded as symbols of the community of interest rather
than a true embodiment of it. "Letters to the Editor" columns in
newspapers and magazines and radio and television call-in
programs are familiar examples.

In contrast, new collaborative media mass forms rely almost
exclusively upon contributions from a wide cross section of
audience members, often with minimal editorial control.
Electronic bulletin board systems, audiotext "chat lines" and
videotext fora are three examples of emerging interactive mass
communication systems in which the audience is also the source of
the content. To understand these new media forms, we must
understand the factors which prompt audience members to make the
contributions needed to make them viable.

Participation in such media is paradoxical, after all.  They are
available to all members in a community of interest, regardless
of whether the individual consumers contribute themselves, and
consumption of the medium does not diminish what is available to
anyone else.  Since no single individual is required to
contribute to the content of the message system in order to
benefit from it, the "rational consumer" might be expected to
adopt the strategy of consuming the medium without making
contributions.  Yet, if no one contributed there would soon be no
medium to consume!  It thus seems that interactivity itself
elicits behavior that transcends the predictions of models of
"rational" economic consumption of information (Rafaeli, 1990;
Rafaeli and Ritchie, 1991).  More formally, this is the dilemma
of so-called "public goods"  (Barry & Hardin, 1982).

How much, why, and when do people contribute to interactive mass
media?  How can we predict, and eventually increase, sharing of
ideas, information, intellectual property, and cognitive work
among peers in communities defined by shared communication
environments? Two theoretical perspectives have emerged recently
which promise to extended our understanding of interactive mass
media forms which rely on the participation of their audiences.

Thorn and Connolly (1987, 1990) developed a theory of
discretionary data bases from the notion of public goods and used
it to predict rates of contribution to stores of information
shared within an organization.  In a series of laboratory
experiments, they found that the lower the perceived value of the
information and the less symmetrical the benefits to users in a
group,  the lower the contribution levels.  Furthermore,
individuals contributed less as participation costs and group
size increased.  However, these results were limited to extremely
small (four or eight person) groups and took place in a
laboratory setting that more closely replicated small workgroup
communication than a mass media context.

Critical Mass theory (Markus, 1987, 1990) takes a parallel
approach, also predicated on the public goods dilemma, which
attempts to explain the growing adoption of interactive media in
a community of interest until a state of near total
participation, or universal access, comes to exist.  The theory
predicts that the chances of attaining universal access are
inversely related to the resource contributions -- in terms of
skill, effort or cost -- required of users.  On the other hand,
the greater the heterogeneity of interests and resources found
among members of a community, the greater the chance of achieving
universal access. Task interdependence, centralization of
resources, group size and geographic dispersion are hypothesized
to be directly related to heterogeneity and hence to adoption.
Critical mass was initially conceptualized with the problem of
adoption of interpersonal communication media -- such as the
telephone and electronic mail -- in mind, but the public goods
argument on which it is based would seem to apply equally well to
collaborative mass media systems.

The two theories thus share common underlying assumptions about
human behavior in contexts in which collaborative behavior is
required to create a communications medium.  They both address
the same general problem of explaining participation in
interactive media that are subject to the dilemma of public
goods. Both paradigms have matching predictions for one key set
of variables relating to the demands placed on the user.  The
more effort, skill, or monetary cost involve, the less the
participation levels.

The two approaches also differ in some important aspects.  Their
independent and dependent variables, units of analysis and the
nature of their predictions are somewhat distinct.

Thorn and Connolly's theory of discretionary data bases focuses
on individual contribution levels as the dependent variable of
interest, operationalized in terms of the percentage of
transactions in which subjects choose to contribute information.
For Markus, the dependent variable is the collaborative adoption
rate in a community of interest, or the percentage of the
community that has adopted the innovation in question.  At a
purely operational level, the distinction is simply that critical
mass focuses on the percentage of a community that uses a
collaborative medium, while the discretionary data base paradigm
examines the subset of users who also make contributions to the
content of the medium.  Presumably, there is also a difference in
the time order of the two outcomes.  Initial adoption behavior --
including the purchase of necessary hardware and software,
obtaining the necessary access codes, logging onto the system for
the first time, etc. -- can be expected to precede contribution

This distinction may in turn explain the differences in
independent variables.  The value of information and the symmetry
of benefits are qualities that can perhaps best be sampled after
initial access has been obtained through the process of adoption,
hence their absence in critical mass theory.   Still, it is
reasonable to expect that users form perceptions of these
qualities even before initial adoption, so that they could be
expected to influence the adoption decision as well.

Note that the critical mass approach makes the opposite
prediction regarding the role of group size.  If larger
communities are also more heterogeneous, then  critical mass
theory predicts that universal access is more likely to be
achieved in larger communities.  Indeed, in this view
participation is not just directly related to group size, it is
exponentially related to the number of participants (cf. Markus,
1987).  Thorn and Connolly (1990, p. 227) argue that large
systems reduce the expectation of reciprocity, and consequently
decrease contribution levels.  Common sense offers a more homely
construction:  the more users there are, the more each user can
safely assume that "someone else will do the job."  This could
even be a positive factor when making an adoption decision.  When
considering whether to adopt a new collaborative medium potential
users may find larger systems more attractive precisely because
they seem to require a lesser investment of resources -- in terms
of their own contributions -- than smaller systems do.

For the purposes of the present research, one possible way to
resolve the distinctions between these two public goods
perspectives is to consider them both to be about the factors
that make collaborative media successful.  The two perspectives
merely focus on different indicators of success.  One defines
success in terms of the proportion of a community of interest
that has adopted the innovation, while the other focuses on the
contribution levels of the participants.

Other outcome variables come to mind, as well.  Since
collaborative media also have mass media characteristics, it is
natural to consider conventional mass media outcome measures,
such as the amount of usage of the system.  In the case of highly
diverse and volatile media, such as the electronic bulletin board
systems considered here, system longevity is another appropriate
outcome measure.

Electronic Bulletin Boards

Electronic bulletin boards marry the twin interests of mass and
interpersonal communication (Rafaeli, 1986).  The first
electronic bulletin board is believed to have gone online in
Chicago, in early 1978 (Anis, 1991).  Today, bulletin board
systems are operated from mainframes as well as stand-alone
personal computer platforms. Some have a narrow, well-defined
areas of interest, while others serve as a general meeting place
for anyone with a personal computer and a modem.  Most boards are
based on audience participation (Rafaeli, 1986; Steinfield &
Fulk, 1988), which makes them an interesting example of
collaborative mass media.  The popular press has been providing
wide, if jaded coverage (e.g. Alexander, 1991; Bromberg, 1991;
USA Today, 1990). The medium has also spawned its own trade
publications, Boardwatch and Plumb.

Between ten and thirty thousand different systems with dozens to
hundreds of participants each are currently in operation in North
America.  Many of these are operated by and for the benefit of
closed groups.  The number of publicly open boards is not known,
however such boards clearly number in the thousands.

The publicly open boards bring the public goods issues into
particularly sharp focus.  Closed boards operating in an
organizational context can easily resort to various forms of
coercion or to monetary incentives to maintain contributions.
Indeed, Thorn and Connolly (1990, p. 226) recommend the latter
strategy to corporate communication managers.  However, the
introduction of these external variables represents a serious
departure from the basic public goods dilemma, which assumes free
choice in the provision of information.  In contrast, public
boards are more nearly a "pure" case of collaborative mass media
in which the exchange of information is in itself the reason
for being.

Most of the attention paid to bulletin board systems by
communication researchers has so far focused on the
characteristics of demand and consumption -- "taking", "getting",
or "Uses and Gratifications" (Chesebro, 1985; Danowski, 1982;
Foulger, 1990; Garramone et al. 1985; 1986a; 1986b; Hellerstein,
1989; Rafaeli, 1986; Rogers and Rafaeli, 1985; Rogers, 1990;
Swift, 1989). However, most published work is based on case
studies of single systems at single points in time, offering
little opportunity to assess variables which affect participation
across systems.

The present research furthers the study of bulletin boards along
the axes of the "hypercube" described in Figure 1.  As noted,
most research to date has been concentrated in one far corner.
They are one-shot case studies, focusing on private or
institutional contexts, devoted to special purposes, and often
experimental in nature.

                      [Figure 1 about here]

Furthermore, bulletin boards represent interactive media which
require contribution as well as consumption of their users.
Studies which focus on usage tend to examine only the "receiving
end" of the interaction.  The public goods concept directs our
attention to the reciprocal "giving" behavior involved in the
operation of the medium.  In the present study, the focus was on
the reciprocity of communication.  The units of analysis were
communities of participants, rather than individual users.

A Model of Collaborative Mass Media Behavior

The present research utilized a model of collaborative mass media
behavior applied to electronic bulletin board systems.  It draws
upon the conceptualizations of discretionary data bases and
critical mass described above. The dependent variables of
interest all relate to the success of electronic bulletin board
systems, described in terms of adoption (after Markus, 1990)
contribution levels (after Thorn and Connolly, 1990), usage and

The independent variables reflect the concerns about resource
requirements, heterogeneity and reciprocity found in public goods
explanations of collaborative media.  In order to assure the
external validity of the findings, an effort was made to
reconstrue management policies identified by "real world"
bulletin board managers into variables which are theoretically
meaningful for collaborative mass media subject to public goods
explanations. These included "exchange rates" instituted to
police the traffic of files, the diversity of content on the
board, and the degree of communication reciprocity maintained.

        H1:     Bulletin board success will be negatively related to
                access restrictions placed on users.

Many bulletin board system managers apply downloading
restrictions on users in an effort to encourage contributions.
One common type of restriction is an upload to download ratio;
e.g. one file must be uploaded for every ten that are downloaded
in order to maintain access privileges.  Another common
restriction is the imposition of time limits on calls in an
effort to keep incoming lines available for other users.  Such
practices increase contribution costs in Thorn and Connolly's
terms, or represent a substantial "communication discipline requirement" in
critical mass terms, and should inhibit both
adoption and contribution levels.  Of course, the imposition of
user fees is perhaps the most obvious example of a contribution
cost or communication requirement that can be expected to limit
bulletin board success.

        H2:     Bulletin board success will be positively related to the
                diversity of content available.

Thorn and Connolly (1990, p. 224) specify the quality of
information, in terms of its value to the user, as an important
determinant of contribution behavior.  At the system level, we
hypothesize that the more diverse the content is, the greater the
likelihood that users will find something of value and will in
turn be prompted to make contributions in order to elicit further
quality contributions.

Critical mass theory does not treat message system content as a
variable, an important oversight, perhaps.  However, we can
deduce from Markus' proposition about heterogeneity of interests
that the more diverse the content, the higher the adoption

The issues of diversity has a somewhat unique meaning in the
world of electronic bulletin boards.  Bulletin board systems
originated as communications media for computer hobbyists and
many maintain this focus, therefore a meaningful indicator of
diversity is the proportion of content devoted to non-computer
related topics.

        H3:     Group size will be negatively related to contribution
                levels but positively related to other measures of bulletin
                board success.

This hypothesis applies Thorn and Connolly's prediction about
contributions and group size to a more externally valid context.
Following critical mass theory, the opposite prediction is made
for adoption levels and other outcome measures of bulletin board

        H4:     Symmetry in contribution levels will be positively
                related to bulletin board success.

Thorn and Connolly state that asymmetries in contribution costs
will reduce contributions.  This means that boards in which a
large proportion of users make contributions to the collaborative
medium should be more successful than those in which only a few
users contribute.  Thorn and Connolly also predict that either
too many contributors or too many non-contributors will reduce
contribution levels.  There needs to be a balance between the two
in their view.

However, unlike the closed organizational systems that Thorn and
Connolly have studied, collaborative mass media are open systems
in which the "problem" of too many contributors could be offset
through the addition of new users to the system.  In view of
this, we hypothesized that collaborative mass media would
demonstrate a direct relationship with symmetry in contributions.

Markus (1987, p. 500) also notes that usage falls off in the
absence of reciprocity.  The proposition about reciprocity in
critical mass theory does not require that the exchange be equal, only that
some number of others reciprocate, however.

                         RESEARCH METHOD


A list of 7600 bulletin boards was constructed from three sources
available in the public domain.  These lists were originally put
together by aficionados, producers of bulletin board software
packages, and operators of bulletin boards.  The collated list
was checked for duplication, resulting in a list of 4800
telephone numbers of electronic bulletin boards. This list thus
constituted the universe of operating, publicly accessible boards
whose operators had attempted to list in national directories.  A
random sample of 500 boards was obtained from the population
list, using a random start and fixed skip interval.


A computer readable questionnaire, consisting of 37 open and
closed ended items, was created.  The questionnaire was uploaded
to the system operators in the sample by calling their user-
access lines. In all, 293 questionnaires were uploaded.  Up to
five callbacks were made to each board in an attempt to upload
the questionnaire. Most calls were made in the late night and
early morning hours, over a period of two months. The remaining
207 numbers included disconnected numbers, constantly busy
numbers, no answers, wrong numbers, voice lines and fax machines.
In addition, about 5 percent of the numbers in the original list
are not included in the final sample because the systems were
closed to the public.

The questionnaire requested system operators to enter their
answers in the spaces provided in the computer-readable
questionnaire form and to post their completed questionnaire on
their bulletin board. Alternatively, operators mailed or faxed
their responses. Approximately three-quarters of the responses
were collected by calling back the systems.  Two call back
attempts were made for each uploaded questionnaire.  There were
126 valid responses, for a completion rate of 42 percent of the
public boards contacted. Twelve percent of the boards refused the

Operational Measures

Five dependent measures relating to the success of electronic
bulletin board systems were defined:

Contribution Level was operationally defined as the ratio of
files contributed, or "uploaded," in a week to the total number
of weekly file transactions, including files uploaded and files
taken, or "downloaded" by users.  Respondents were asked, "How
many files UPLOADED[DOWNLOADED] in an average week?" and these
estimates were used to compute the ratio.  This measure
corresponds closely to that in the Thorn and Connolly (1990)
experiments, in which the percentage of experimental transactions
in which information was contributed was the dependent variable.

Adoption Rate was the ratio of regular callers ("How many REGULAR
callers who call at least once a week") to the total number of
users ("How many DIFFERENT callers do you estimate you have.")
It measures the adoption of the system among the community of
interest defined by each board.

Longevity was the answer to the question, "How many months ago
did this board first go on line?"

Usage was the "Average number of calls on an average day."

Independent variables relating to user restrictions, diversity,
group size and communication symmetry were also defined:

Ratio Restriction was a dichotomous variable, scored 1 if the
board operator had upload-download restrictions, 0 if not.
Replies to the question "What are your policies about
upload/download ratios and how have they changed over time" were
coded in this fashion.

Time Restriction was the response to the question, "What is the
online time limit?" Thus, in this case, the higher the number,
the less restrictive the policy.

Fee Requirement was scored 1 if the operator indicated that any
revenues were derived from recurring user fees or usage fees, 0
if no user fees were required.

Diversity was defined as the response to the question, "What
percent of the content on your board would you say is NOT
computer related?"

Group Size was the total size of the community of interest ("How
many DIFFERENT callers do you estimate you have?")

Symmetry was the percentage of board users characterized by the
board operator as being either "givers" ("who share knowledge and
resources") or "exchangers" ("participating in a fair exchange"),
as opposed to "Takers" ("who are looking for 'something for

Additional questions about the characteristics of boards, their
activity levels and management practices were also included in
the survey.  Open ended-questions about purpose ("How do you
define the purpose of your board?"), scope ("How do you describe
your target community?") and success factors ("What do YOU think
makes a bulletin board system successful?") were included to
further discern the nature of bulletin board activity.


Usable responses were received from 126 boards located in forty-
five different states.  Some of the boards were quite long-lived,
including one that was eleven years old at the time of the
survey, and twenty-five percent of those surveyed were over five
years old. Thirteen percent had been in existence for only a year
or less. The average longevity was about three and a half years
(41.6 months).  On average, thirty-eight percent of the weekly
file transactions involved the contribution of files from users.
An average of eighteen percent of the boards' user universe
(defined as the number of different callers) are active users,
placing calls on a weekly basis.  Slightly over fifty calls per
week are made to the typical board in the survey, but the range
is quite wide.  One of the boards reported 2000 weekly calls.

The average user community served included nearly 900 (886.9)
different users.  The boards surveyed were very diverse in terms
of the nature and scope of their target audiences.  The boards
included in the sample ranged from general purpose systems available to all
computer users (39%) to highly specialized
systems dedicated to specific groups.  Twenty percent of the
system operators said that their boards were either national or
international in scope.  The specific audiences cited included
computer professionals, handicappers, children, lawyers, ham
radio operators, AIDS professionals and victims, physics
researchers. Sixteen percent of the boards identified upper class
(i.e., high income or highly educated) individuals as their
target audience.

Bulletin board systems are defined as much by the nature of their
content as by the characteristics of their audiences.  Some of
the more highly specialized systems in the sample included public
boards operated by large corporations and service organizations
and product support bulletin boards for software companies.  Of
course, all board users share an interest in computing, since a
personal computer or terminal is required for access.  On
average, about two-thirds of board content is devoted to
computer-related matters, but only nine percent of the boards
were exclusively computer related.  In contrast, twenty-two
percent of the boards said that half or more of board content was
unrelated to computer topics.

Abuse is an important issue for board operators.  Common abuses
include evasion of rules against excessive downloading and
lengthy sessions that tie up incoming lines, the uploading of
"junk" files and the placement of obscene or abusive messages on
the boards. Over two-thirds of the boards in the sample reported
instances of abusers.  The most common policy for dealing with
such abuse was the termination of access rights.  Fewer operators
reduced access rights, and only about half limited downloading.
The least popular strategy was notification of the police,
reported by one in seven operators.

A wide variety of board management policies are in effect to
forestall such problems.  Twenty-three percent of the boards said
they charged either recurring or per transaction fees to users.
Forty-one percent enforce some form of download ratio in an
attempt to curb "selfish" users who merely take files without
offering up files of their own.  Time limits were in effect for
all but six percent of the boards.  The average maximum length of
call allowed was about an hour (55.6 minutes).  The longest time
limit was two hours.  In fact, 44 percent of all boards surveyed
had a time limit set at exactly 60 minutes.  Furthermore, most
board operators award access time by user status.  Less than half
credit additional time based on upload history, and about a third
allow users to purchase access time.  Other access policies
included preferential treatment for visiting operators from other
systems, time of day differentials, and the award of more time
upon request.

Another mark of successful board management is the ability to
develop active participation.  When asked to classify their users
as "Givers", "Exchangers", or "Takers", system operators
classified more of their users as "Takers", than either of the
other two categories.  The median percentage assigned to "Takers"
was 50 percent, while the median for each of the other, 'less
selfish' categories was 20 percent.

The "art" of running a bulletin board is still being defined.
When asked to describe factors in the success of bulletin board
systems, the most frequently cited factor was the responsiveness
of the system operator to user needs, which was mentioned by
twenty-three percent of the respondents.  The quantity of files
available and the quantity of user contributions were each cited
by nineteen percent of the respondents.

Table 1 displays means, standard deviations and correlation
coefficients for the dependent and independent variables used to
test the hypotheses for the present study.  The dependent
measures of system success were generally not very highly
correlated. The only significant correlation among the measures
of system success was a negative correlation between contribution
levels and system longevity (Pearson r=-.21, p < .05).
Accordingly, the patterns of relationships with the independent
variables were considered separately for each of the indicators
of system success.

Contribution levels were not significantly related to the
presence of upload-download ratio restrictions, time
restrictions, or the imposition of user fees.  The relationships
to transaction ratios, time restrictions and fee policies were in
the directions hypothesized, even though they were not
significant.  Content diversity was directly related to
contribution levels, as hypothesized (r=.27, p < .01), as was
symmetry in contribution levels (r=.22, p < .05).  Group size was
not significantly related to contribution levels, although again
the relationship was at least in the direction expected.

Adoption levels, defined in terms of the proportion of regular
users among the total community of users, were negatively related
to group size (r=-.33, p < .01), the opposite direction of what
was predicted from critical mass theory.  Symmetry in
contribution activity was positively related to adoption levels
(r=.30, p < .01), as expected.  The other hypotheses were not
supported and the directionalities of the relationships observed
were generally opposite those predicted.  The exception was that
leniency in access time restrictions was positively related to
adoption levels, which was the direction hypothesized.

The longevity of the boards surveyed was positively related to
group size, as predicted (r=.40, p < .01), but the other
hypothesized relationships were not supported.  Only the
prediction about content diversity was in the anticipated

Finally, weekly usage levels were directly related to group size
as hypothesized (r=.27, p < .01), but were positively correlated
to the existence of a fee policy (r=.19, p < .01), contrary to
expectation.  The other relationships were not only not
significant, but tended to be in the opposite of their predicted


The exchange of files and messages occurring on electronic
bulletin board systems has a mass communication flavor to it.  It
has been occurring on a fairly large scale for well over a
decade.  Unlike traditional mass media vehicles which involve
one-to-many dissemination of content, bulletin boards are
collaborative efforts defined by a many-to-many relationship.
The members of the community of interest participate in the
creation of the message. Such participation is of both practical
and theoretical import.

It appears that structural characteristics of collaborative mass
media systems seem to be more critical to their success than
specific management policies applied by system operators.  The
diversity of content and the symmetry of exchange between participants were
the most important of the factors derived from
public goods theories which predict bulletin board system
success. The day-to-day operating restrictions placed on users --
including upload ratios, access time restrictions and user fees
-- generally had little relationship to measures of board

The above statement must be heavily qualified according to which
measure of success is in question.  The predictions of public
goods theory best explained contribution levels, but did not seem
to be a "good fit" for the other outcome measures of adoption,
longevity and usage.  The results were not very robust even for
contribution levels.  Perhaps there are distinct processes which
uniquely explain these different aspects of collaborative mass
media systems, apart from public goods explanations.

It seems that the predictions of public goods theories need
further refinement when applied to collaborative mass media.  In
somewhat of a challenge to Public Goods theory, and mild support
of Critical Mass theory, symmetry in user contribution behavior
was related positively to both contribution and adoption rates.
It may be that the open-ended nature of public collaborative
media makes them a different case from collaborative media that
exist in closed group settings, such as in organizations.  When a
public board is the beneficiary of exceptional contributions from
users, there is a ready supply of new users who will be attracted
and offset any problems with the "over-supply" of information.
The present results perhaps indicate a need to re-assess the
importance of symmetry in contributions from user groups in open
media systems.

The picture emerging from these data is of a more complex world
than predicted by either theory.  There were small-scale,
rationally managed, tightly economical (or exchange-governed)
boards, where the public goods of information were traded.  At
the same time, many other boards exist and survive, where the
emphasis is on diversity, numerous callers, and generalized
reciprocity expectations rather than tightly managed quantitative
exchange rates.

In future research it would be worthwhile to re-conceptualize and
test some other system management issues in public goods terms.
In the present sample of system operators, their own
responsiveness, the quantity of files available and the quantity
of user contributions were deemed the most important factors in

The operator, as "the master user," has the ability to control
the symmetry of the exchange through her own contributions to the
board.  This might be especially true of smaller boards, in which
an active system operator could affect the gross exchange rate in
meaningful ways.  In such cases, the expertise of the operator
and the centralization of resources represented by that person
could create the "heterogeneity of resources" which critical mass
theory holds is an important driver of universal access.

The quantity of files available also has meaning in public goods
theories.  The larger the file library, the more likely that
"heterogeneity of interests" may be obtained, in critical mass
terms, driving user adoption.  Thorn and Connolly's theory of
discretionary data base contributions would seem to make the
opposite prediction with respect to contribution levels:  Faced
with a wide array of valuable files, individual users might be
discouraged from making contributions of their own.  The chances
of inducing others to contribute by offering files that only make
a marginal addition to an already expansive data base would seem to be slight,
so contribution behavior should be inhibited by the
sheer volume of files available.

While on the topic of system content, this seems to be another
area worthy of further consideration by public goods theorists.
In the current research, the diversity of content was related to
contribution levels, although not to adoption rates.  There is
room for much refinement of the content diversity variable, such
as defining it in relation to the number of different topics
carried and the number of files devoted to each.  The quality of
the content should also be an important factor, although it is
difficult to imagine a satisfactory measure of quality that could
be assessed at the system level.

The final "success factor" identified by the system operators --
the quantity of files contributed -- suggests that there may be
an order of precedence among the various success factors examined
in the present research.  A healthy contribution rate may be a
precondition of universal access within a community of interest.

The "Community of Interest" Problem

Overall, critical mass theory found only slight support,
correctly predicting that adoption levels would be related to
reciprocity between users.  An important caveat on the present
findings as they apply to critical mass theory is that the
dependent measure of adoption used here -- the ratio of regular
users to the total number of different callers -- was not
entirely satisfactory.

For collaborative mass media systems, it is difficult to specify
"community of interest," the denominator used to calculate the
adoption rate in critical mass theory.  Part of the problem is
that electronic bulletin board use entails a cluster of
innovations, not a single innovation.  One must first adopt home
computer technology, then data communications and then the
behavior of searching bulletin board systems before one is in the
community of interest.  Further restrictions could be placed on
the definition of the community according to the thematic content
of the boards and the characteristics of their target audiences.
The community of interest could perhaps then be defined as
"People with personal computers and computer modems who access
bulletin board systems and who are interested in the topics that
the board specialized in."

In any event, the system operators who participated in the study
apparently had no way to meaningfully estimate the size of their
communities of interest.  When asked to identify their target
populations, most seemed to base their estimates on the total
population of their local calling areas.  The use of these
estimates did not seem appropriate as they would have made the
adoption rates too dependent upon a third variable:  the size of
the board's municipality of origin.

At least one of the contrary findings of the present study may
have been due to the nature of the adoption rate measure that was
used. The adoption rate was a simple transformation of the group
size variable.  Group size was in the denominator of the adoption
rate measure, so it was no surprise that the two were negatively

The definition of the community of interest is likely to remain a
thorny issue in future investigations of collaborative mass media
that are publicly offered.  By their very nature, collaborative
mass media have self-defining communities of interest.  The very
act of accessing a bulletin board system is what defines one both as a member
of the community of interest and as an adopter of the

For Further Research

This study had some important limitations that should be
addressed by future research.  We restricted ourselves to public
boards, and the sampling strategy included only boards that were
in operation at the time of the study.  A resulting limitation of
the sampling scheme was that only successful boards participated,
restricting the range of validity of our claims.  Perhaps we
failed to note the effect of critical mass for the simple reason
that systems who failed to achieve critical mass had already
failed and "selected themselves" out of the sample.  The results
reported here may merely indicate that the bulletin board system
medium has not yet reached the "stable state" cited as an
important milestone in critical mass theory.  Future studies
should employ time series methods to examine over-time effects of
the independent variables on community adoption rates within
individual bulletin board systems.

This study was also subject to many of the problems of self-
report surveys.  Some of the responses, most notably estimates of
financial resources and growth patterns, were so riddled with
apparent inconsistencies that we chose not to include them.
However, some of the data was at least machine-generated, if
still self-reported.  In many cases the software used to operate
the boards also provided objective statistics about specific
items including the number of callers and file activity levels.
In several instances, system operators even appended computer
files of usage statistics that were automatically generated by
their operating software.

An innovative approach to overcoming these limitations would be
to create "experimental boards," in which variables of board
management policy could be carefully controlled and manipulated
and their effects on system success evaluated with machine-
generated data.  Such an approach could achieve a satisfactory
degree of experimental control in a context that has a high
degree of external validity, while eliminating the possible
biases of self- reported data.  There would also be the
opportunity to survey board users so that key assumptions about
the linkage between individual and system-level variables (e.g.,
that users are capable of perceiving symmetry in contribution
levels) could be verified.

In conclusion, the documentation of the type of collaborative
media behavior represented by bulletin board systems remains an
important topic.  Bulletin boards have outlived many of the
failed videotext experiments, so far without attracting as much
attention.  The focus on the unit of analysis of entire
communities of users is also important methodologically.  The
study of interactive technologies needs to proceed beyond the
case-study level in hopes of discerning the factors that lead to
the success or failure of collaborative mass media systems.

                             TABLE 1



 VARIABLE    Mean  S.D. 2    3    4    5    6    7    8    9

   1         Contributions   .38  .29   .06 -.21*     -.11 -.13
.00          -.03   .27+     -.07 .22*
 2 Adoption  .18   .15       -.12 -.07  .11  .14  .00 -.04 -.33+
 3 Longevity 41.61 26.17                .11  .12 -.15  .07  .11
.40+         -.09
 4 Usage     51.69 183.00                    .12  .00  .19*     -
.02           .27+ -.07
 5 Ratio Restricted     .41  .49                      -.01  .38+
-.18         -.09   .09
 6 Time Restricted 55.52     25.59                              -
.06          -.02  -.23*      .15
 7 Fee Restricted  .23  .42                                -.26+
.06          -.23*
 8 Diversity 31.58 30.49
.14           .15
 9 Group Size      886.91    1198.85
 10          Symmetry   51.39     31.33

Note:  Table entries are Pearson Product-Moment correlations.
* p < .05  + p < .01


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