electronic bulletin board is believed to have gone online inChicago, in early 1978 (Anis, 1991).  Today, bulletin boardsystems are operated from mainframes as well as stand-alonepersonal computer platforms. Some have a narrow, well-definedareas of interest, while others serve as a general meeting placefor anyone with a personal computer and a modem.  Most boards arebased on audience participation (Rafaeli, 1986; Steinfield &Fulk, 1988), which makes them an interesting example ofcollaborative mass media.  The popular press has been providingwide, if jaded coverage (e.g. Alexander, 1991; Bromberg, 1991;USA Today, 1990). The medium has also spawned its own tradepublications, Boardwatch and Plumb.Between ten and thirty thousand different systems with dozens tohundreds of participants each are currently in operation in NorthAmerica.  Many of these are operated by and for the benefit ofclosed 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 intoparticularly sharp focus.  Closed boards operating in anorganizational context can easily resort to various forms ofcoercion or to monetary incentives to maintain contributions.Indeed, Thorn and Connolly (1990, p. 226) recommend the latterstrategy to corporate communication managers.  However, theintroduction of these external variables represents a seriousdeparture from the basic public goods dilemma, which assumes freechoice in the provision of information.  In contrast, publicboards are more nearly a "pure" case of collaborative mass mediain which the exchange of information is in itself the reasonfor being.Most of the attention paid to bulletin board systems bycommunication researchers has so far focused on thecharacteristics 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 casestudies of single systems at single points in time, offeringlittle opportunity to assess variables which affect participationacross systems.The present research furthers the study of bulletin boards alongthe 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 orinstitutional contexts, devoted to special purposes, and oftenexperimental in nature.                      [Figure 1 about here]Furthermore, bulletin boards represent interactive media whichrequire contribution as well as consumption of their users.Studies which focus on usage tend to examine only the "receivingend" of the interaction.  The public goods concept directs ourattention to the reciprocal "giving" behavior involved in theoperation of the medium.  In the present study, the focus was onthe reciprocity of communication.  The units of analysis werecommunities of participants, rather than individual users.A Model of Collaborative Mass Media BehaviorThe present research utilized a model of collaborative mass mediabehavior applied to electronic bulletin board systems.  It drawsupon the conceptualizations of discretionary data bases andcritical mass described above. The dependent variables ofinterest all relate to the success of electronic bulletin boardsystems, described in terms of adoption (after Markus, 1990)contribution levels (after Thorn and Connolly, 1990), usage andlongevity.The independent variables reflect the concerns about resourcerequirements, heterogeneity and reciprocity found in public goodsexplanations of collaborative media.  In order to assure theexternal validity of the findings, an effort was made toreconstrue management policies identified by "real world"bulletin board managers into variables which are theoreticallymeaningful for collaborative mass media subject to public goodsexplanations. These included "exchange rates" instituted topolice the traffic of files, the diversity of content on theboard, 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 downloadingrestrictions 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 downloadedin order to maintain access privileges.  Another commonrestriction is the imposition of time limits on calls in aneffort to keep incoming lines available for other users.  Suchpractices increase contribution costs in Thorn and Connolly'sterms, or represent a substantial "communication discipline requirement" incritical mass terms, and should inhibit bothadoption and contribution levels.  Of course, the imposition ofuser fees is perhaps the most obvious example of a contributioncost or communication requirement that can be expected to limitbulletin 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 ofinformation, in terms of its value to the user, as an importantdeterminant of contribution behavior.  At the system level, wehypothesize that the more diverse the content is, the greater thelikelihood that users will find something of value and will inturn be prompted to make contributions in order to elicit furtherquality contributions.Critical mass theory does not treat message system content as avariable, an important oversight, perhaps.  However, we candeduce from Markus' proposition about heterogeneity of intereststhat the more diverse the content, the higher the adoptionlevels.The issues of diversity has a somewhat unique meaning in theworld of electronic bulletin boards.  Bulletin board systemsoriginated as communications media for computer hobbyists andmany maintain this focus, therefore a meaningful indicator ofdiversity is the proportion of content devoted to non-computerrelated 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 aboutcontributions and group size to a more externally valid context.Following critical mass theory, the opposite prediction is madefor adoption levels and other outcome measures of bulletin boardsuccess.        H4:     Symmetry in contribution levels will be positively                related to bulletin board success.Thorn and Connolly state that asymmetries in contribution costswill reduce contributions.  This means that boards in which alarge proportion of users make contributions to the collaborativemedium should be more successful than those in which only a fewusers contribute.  Thorn and Connolly also predict that eithertoo many contributors or too many non-contributors will reducecontribution levels.  There needs to be a balance between the twoin their view.However, unlike the closed organizational systems that Thorn andConnolly have studied, collaborative mass media are open systemsin which the "problem" of too many contributors could be offsetthrough the addition of new users to the system.  In view ofthis, we hypothesized that collaborative mass media woulddemonstrate a direct relationship with symmetry in contributions.Markus (1987, p. 500) also notes that usage falls off in theabsence of reciprocity.  The proposition about reciprocity incritical mass theory does not require that the exchange be equal, only thatsome number of others reciprocate, however.                         RESEARCH METHODSamplingA list of 7600 bulletin boards was constructed from three sourcesavailable in the public domain.  These lists were originally puttogether by aficionados, producers of bulletin board softwarepackages, and operators of bulletin boards.  The collated listwas checked for duplication, resulting in a list of 4800telephone numbers of electronic bulletin boards. This list thusconstituted the universe of operating, publicly accessible boardswhose operators had attempted to list in national directories.  Arandom sample of 500 boards was obtained from the populationlist, using a random start and fixed skip interval.ProcedureA computer readable questionnaire, consisting of 37 open andclosed ended items, was created.  The questionnaire was uploadedto the system operators in the sample by calling their user-access lines. In all, 293 questionnaires were uploaded.  Up tofive callbacks were made to each board in an attempt to uploadthe questionnaire. Most calls were made in the late night andearly morning hours, over a period of two months. The remaining207 numbers included disconnected numbers, constantly busynumbers, no answers, wrong numbers, voice lines and fax machines.In addition, about 5 percent of the numbers in the original listare not included in the final sample because the systems wereclosed to the public.The questionnaire requested system operators to enter theiranswers in the spaces provided in the computer-readablequestionnaire form and to post their completed questionnaire ontheir bulletin board. Alternatively, operators mailed or faxedtheir responses. Approximately three-quarters of the responseswere collected by calling back the systems.  Two call backattempts were made for each uploaded questionnaire.  There were126 valid responses, for a completion rate of 42 percent of thepublic boards contacted. Twelve percent of the boards refused thesurvey.Operational MeasuresFive dependent measures relating to the success of electronicbulletin board systems were defined:Contribution Level was operationally defined as the ratio offiles contributed, or "uploaded," in a week to the total numberof weekly file transactions, including files uploaded and filestaken, or "downloaded" by users.  Respondents were asked, "Howmany files UPLOADED[DOWNLOADED] in an average week?" and theseestimates were used to compute the ratio.  This measurecorresponds closely to that in the Thorn and Connolly (1990)experiments, in which the percentage of experimental transactionsin which information was contributed was the dependent variable.Adoption Rate was the ratio of regular callers ("How many REGULARcallers who call at least once a week") to the total number ofusers ("How many DIFFERENT callers do you estimate you have.")It measures the adoption of the system among the community ofinterest defined by each board.Longevity was the answer to the question, "How many months agodid 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 theboard operator had upload-download restrictions, 0 if not.Replies to the question "What are your policies aboutupload/download ratios and how have they changed over time" werecoded in this fashion.Time Restriction was the response to the question, "What is theonline 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 anyrevenues were derived from recurring user fees or usage fees, 0if no user fees were required.Diversity was defined as the response to the question, "Whatpercent of the content on your board would you say is NOTcomputer related?"Group Size was the total size of the community of interest ("Howmany DIFFERENT callers do you estimate you have?")