the quantity of files contributed -- suggests that there may bean order of precedence among the various success factors examinedin the present research.  A healthy contribution rate may be aprecondition of universal access within a community of interest.The "Community of Interest" ProblemOverall, critical mass theory found only slight support,correctly predicting that adoption levels would be related toreciprocity between users.  An important caveat on the presentfindings as they apply to critical mass theory is that thedependent measure of adoption used here -- the ratio of regularusers to the total number of different callers -- was notentirely satisfactory.For collaborative mass media systems, it is difficult to specify"community of interest," the denominator used to calculate theadoption rate in critical mass theory.  Part of the problem isthat electronic bulletin board use entails a cluster ofinnovations, not a single innovation.  One must first adopt homecomputer technology, then data communications and then thebehavior of searching bulletin board systems before one is in thecommunity of interest.  Further restrictions could be placed onthe definition of the community according to the thematic contentof 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 accessbulletin board systems and who are interested in the topics thatthe board specialized in."In any event, the system operators who participated in the studyapparently had no way to meaningfully estimate the size of theircommunities of interest.  When asked to identify their targetpopulations, most seemed to base their estimates on the totalpopulation of their local calling areas.  The use of theseestimates did not seem appropriate as they would have made theadoption rates too dependent upon a third variable:  the size ofthe board's municipality of origin.At least one of the contrary findings of the present study mayhave been due to the nature of the adoption rate measure that wasused. The adoption rate was a simple transformation of the groupsize variable.  Group size was in the denominator of the adoptionrate measure, so it was no surprise that the two were negativelycorrelated.The definition of the community of interest is likely to remain athorny issue in future investigations of collaborative mass mediathat are publicly offered.  By their very nature, collaborativemass media have self-defining communities of interest.  The veryact of accessing a bulletin board system is what defines one both as a memberof the community of interest and as an adopter of theservice.For Further ResearchThis study had some important limitations that should beaddressed by future research.  We restricted ourselves to publicboards, and the sampling strategy included only boards that werein operation at the time of the study.  A resulting limitation ofthe sampling scheme was that only successful boards participated,restricting the range of validity of our claims.  Perhaps wefailed to note the effect of critical mass for the simple reasonthat systems who failed to achieve critical mass had alreadyfailed and "selected themselves" out of the sample.  The resultsreported here may merely indicate that the bulletin board systemmedium has not yet reached the "stable state" cited as animportant milestone in critical mass theory.  Future studiesshould employ time series methods to examine over-time effects ofthe independent variables on community adoption rates withinindividual bulletin board systems.This study was also subject to many of the problems of self-report surveys.  Some of the responses, most notably estimates offinancial resources and growth patterns, were so riddled withapparent inconsistencies that we chose not to include them.However, some of the data was at least machine-generated, ifstill self-reported.  In many cases the software used to operatethe boards also provided objective statistics about specificitems including the number of callers and file activity levels.In several instances, system operators even appended computerfiles of usage statistics that were automatically generated bytheir operating software.An innovative approach to overcoming these limitations would beto create "experimental boards," in which variables of boardmanagement policy could be carefully controlled and manipulatedand their effects on system success evaluated with machine-generated data.  Such an approach could achieve a satisfactorydegree of experimental control in a context that has a highdegree of external validity, while eliminating the possiblebiases of self- reported data.  There would also be theopportunity to survey board users so that key assumptions aboutthe linkage between individual and system-level variables (e.g.,that users are capable of perceiving symmetry in contributionlevels) could be verified.In conclusion, the documentation of the type of collaborativemedia behavior represented by bulletin board systems remains animportant topic.  Bulletin boards have outlived many of thefailed videotext experiments, so far without attracting as muchattention.  The focus on the unit of analysis of entirecommunities of users is also important methodologically.  Thestudy of interactive technologies needs to proceed beyond thecase-study level in hopes of discerning the factors that lead tothe success or failure of collaborative mass media systems.                             TABLE 1                   DESCRIPTIVE STATISTICS AND            PEARSON PRODUCT-MOMENT CORRELATION MATRIX___________________________________________________________________________________________________________________________________ VARIABLE    Mean  S.D. 2    3    4    5    6    7    8    910___________________________________________________________________________________________________________________________________   1         Contributions   .38  .29   .06 -.21*     -.11 -.13.00          -.03   .27+     -.07 .22* 2 Adoption  .18   .15       -.12 -.07  .11  .14  .00 -.04 -.33+.30+ 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 -.22* 10          Symmetry   51.39     31.33_________________________________________________________________________________________________________________________Note:  Table entries are Pearson Product-Moment correlations.* p < .05  + p < .01                            REFERENCESAlexander, M. 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