Table 3a.

Example of calculating the PPG score for a vaccine confidence boosting belief

Belief: “If I get the vaccine, I will help protect other vulnerable people in my community.”
		Strong believers (=Strong agree/somehow agree)	Potential believers (=all other responses)	Overall	Potential Percentage to Gain
Whole sample	% Vaccine acceptance = 1	93.5%	28.8%	79.1%	PPG = 93.5–79.1 = 14.4%
	% Believers in targeted population	77.7%	22.3%
Urban	% Vaccine acceptance = 1	94.2%	39.4%	84.5%	PPG = 94.2–84.5 = 9.7%
	% Believers in targeted population	82.4%	17.6%
Rural	% Vaccine acceptance = 1	93.2%	25.3%	75.6%	PPG = 93.2–75.6 = 17.6%
	% Believers in targeted population	76.6%	23.4%
Clinical staff	% Vaccine acceptance = 1	94.3%	28.6%	81.3%	PPG = 94.3–81.3 = 13%
	% Believers in targeted population	80.2%	19.8%
Non-clinical staff	% Vaccine acceptance = 1	92.7%	28.9%	77.1%	PPG = 92.7–77.1 = 15.6%
	% Believers in targeted population	75.5%	24.5%

Notes. For the whole sample, the conditional probability of being vaccine endorsers (i.e., vaccine acceptance = 1) among the strong believers (i.e., strongly agree or somewhat agree with the belief item) was estimated to be 93.5%. The conditional probability of being vaccine endorsers among the potential believers (i.e., reporting lower levels of agreement with the belief item) was estimated to be 79.1%. The marginal probability of being vaccine endorsers in the targeted population—which, in this case referred to the entire sample—was estimated to be 79.1%. Then, for the whole sample, the PPG score was calculated as 93.5%−79.1% = 14.4%.

In this example, the total proportion of strong believers in the whole sample was estimated to be 77.7% and the corresponding estimated proportion for potential believes was 22.3%. These proportions were informative but not necessary for calculating the PPG score. For other sub-groups (urban, rural, clinical staff, non-clinical staff), targeted PPG scores were provided following the same formula.