A Multilevel Event History Model of Social Diffusion: Medical Innovation Revisited

Abstract

This article presents a multilevel event history model of social diffusion and applies it to Coleman, Katz, and Menzel's (1966) data on the adoption of tetracycline by physicians. The simplest form of a multilevel model allows a random intercept. In the present application of this simple model to the Medical Innovation data, structured for an event history analysis, the physicians are nested in city and time. Random intercepts capture effects of contextual conditions that are shared by event history cases with the same city–time status. The intercepts also reflect any baseline internal contagion effects, that is, the proportion of physicians in the city–time network who have adopted the drug at time t − 1. Here, I show that Van den Bulte and Lilien's (2001) finding of an important contextual effect of drug firms' marketing effort is misleading. I also show that the social network in which physicians are situated significantly contributes to their adoptions, controlling for baseline internal contagion effects and individual-level characteristics of physicians, which have been emphasized in investigations of these data.

Keywords:

• contagion
• diffusion
• social networks

ACKNOWLEDGMENTS

I am grateful to David Strang and Nancy Tuma for comments on drafts of this article, and to Christophe Van de Bulte for providing the data on which the present analysis is based.

Notes

*p < .10; **p < .05; ***p < .01; ****p < .001 (two-sided).

†In Van den Bulte and Lilien's data set, the social contagion measures are denoted TOTCOH, BURTCOH, TOTSP, and BURTSE1, respectively, for Models 1b, 2b, 3b, and 4b. See their 2001 article on the construction of these measures.

*p < .10; **p < .05; ***p < .01; ****p < .001 (two-sided).

†LR test vs. logistic regression: chi2(2) = 4.2E − 12, Prob > chi2 = 1.0000.

††CNET is measured as the mean of the four network contagion measures employed in Van den Bulte and Lilien's analysis, i.e., TOTCOH, BURTCOH, TOTSP, and BURTSE1 in Table 2, for which Cronbach's α is 0.922.

Note: These estimates are based on Stata 10's xtmelogit procedure.