The effectiveness of pay-it-forward in addressing HPV vaccine delay and increasing uptake among 15–18-year-old adolescent girls compared to user-paid vaccination: a study protocol for a two-arm randomized controlled trial in China

Table 1 Sample size calculation

	Sample size	Sample size (non-response and/or dropout rate of 10%)	ɑ	β
Pay-it forward arm	120	133
Standard-of-care arm	120	133
Total	240	266	0.05	0.20

ISSN: 1471-2458