Table 4.

Effects of Source Credibility as a Function of Attitude Formation Versus Change and Message Repetition

	Attitude formation			Attitude change
Variable	Immediate impact (d+)	Delayed impact (d+)	Impact change (Δ+)	Immediate impact (d+)	Delayed impact (d+)	Impact change (Δ+)
Message repetition
No repetition	0.78	0.27	−0.51	0.27	0.17	−0.11
	(0.58 to 0.98)	(0.09 to 0.45)	(−0.64 to −0.37)	(0.21 to 0.34)	(0.10 to 0.24)	(−0.16 to −0.06)
	Qw = 9.26, ns	Qw = 6.08, ns	Qw = 27.59**	Qw = 61.90***	Qw = 41.72*	Qw = 77.43***
		k=10			k= 29
Message repeated	0.53	0.37	−0.16	—	—	—
	(0.37 to 0.69)	(0.21 to 0.54)	(−0.28 to −0.04)
	Qw = 12.55, ns	Qw = 28.88**	Qw = 34.66***	—	—	—
		k=14
Between-group differences (QB)	3.61†	0.73, ns	16.78***	—	—	—

Note. The immediate and delayed impact of source credibility was calculated by subtracting mean persuasion for low-credibility sources from mean persuasion for high-credibility sources. Positive effect sizes indicate that highly credible sources induced greater persuasion than did less credible sources. The effect sizes in the impact change columns were computed by subtracting the immediate impact of source credibility from the delayed impact. These effect sizes are all negative because the impact of source credibility decayed over time, in general. The Q_w statistic is an index of homogeneity of effect sizes within a given cell. Significant Q_w values indicate violations of the homogeneity assumption. The between-classes effect (Qb) is a sum of squares analogous to a main effect in a fixed-effects ANOVA test (Hedges & Olkin, 1985). k= number of studies; d₊ and Δ₊ = weighted average effect size; CI = confidence interval around d₊ or Δ₊.

^†p < .06.

^*p < .05.

^**p < .01.

^***p < .001.