Meta-analysis 1
Testing Inoculation Theory: A Meta-Analysis
Inoculation theory, described by Eagly and Chaiken as “the grandparent theory of
resistance to attitude change” (1993, p. 561), has been the focus of considerable research interest
in the past two decades. Inoculation theory applies the biological methaphor to conferring
resistance to persuasion by using preemptive messages that “inoculate” individuals against future
influence messages (Compton & Pfau, 2005; McGuire & Papageorgis, 1961). During this time,
research has focused on uncovering the mechanisms behind inoculation theory as well as
investigating inoculation’s potential applications in health, political, and commercial contexts.
Research examining inoculation theory has been successful at revealing several “nuances” (Pfau,
et al. 1997) in the process while simultaneously demonstrating inoculation theory’s almost
limitless application (e.g., An & Pfau, 2004; Burgoon, Pfau & Birk; 1995; Compton & Pfau,
2004); however, there remain important theoretical questions that lack clear answers.
The meta-analysis reported here examined several key theoretical questions regarding
inoculation theory. First, despite the plethora of tests of inoculation, there is some inconsistency
regarding the effectiveness of inoculation theory to confer resistance to attitude change.
Although a fair amount of support exists for the theory (e.g., McGuire, 1961a, 1961b, 1962,
1964, 1966; McGuire & Papageorgis, 1961, 1962; Papageorgis & McGuire, 1961; Pfau, Holbert,
Pasha, & Lin, 2000; Pfau et al., 1997a, 1997b, 2001a, 2003, 2004, 2005; Wood, 2007), others
studies showed no difference in the attitudes of inoculation participants and those individuals in
the control condition (e.g. Lessne, 1983; Pashupati et al., 2002). Conducting a meta-analysis
makes it possible to determine the aggregate effect size for the body of research on inoculation
theory and, thus, offers a more comprehensive evaluation than any single test of the theory.
Second, the substantial amount of research conducted on inoculation theory has revealed several
potential moderating variables, and no single experiment can resolve the discrepancies and