Trial design, eligibility, randomization and recruitment
WEST, RECRUITMENT
Working with the district offices of the Ministry of Health, we selected one region (Central) and six districts that were scheduled to have COVID-19 vaccine supplies made available in January–February 2022. Vaccine supplies were being made available on a district-by-district basis in Ghana. The six districts in our sample are:District 1: Gomoa West – Central RegionDistrict 2: Asikuma Odoben Brakwa – Central RegionDistrict 3: Twifo Ati-Morkwaa – Central RegionDistrict 4: Assin North – Central RegionDistrict 5: Asugyaman – Central RegionDistrict 6: Upper Manya Krobo – Central RegionTo ensure that we would have adequate power for the COVID-19 vaccine outcomes, we randomized at the village level to generate experimental variation for each set of outcomes. The CONSORT diagram (Fig. Working with our partners in each district, we identified the list of district villages that could feasibly be enumerated by our enumeration team (the primary consideration here was either road access or the quality of the road access). Then, within each district, we generated a complete list of the villages that are candidates for enumeration. The villages were then ranked according to their population size (population statistics provided by the 2010 Ghana census). We then formed groups of four villages by putting four consecutive villages on these lists in the same quadruplet. In a typical district, we would have approximately 50 quadruplets.In each district, we randomly selected 13 quadruplets with probabilities weighted by the quadruplet’s share of the total population of the villages being considered in the district. This initial sample of quadruplets was then adjusted in consultation with the district health officials. The adjusted selection criteria are driven, in part, by cost considerations; for budget reasons, we were constrained to ensure reasonable travel distances between the four village clusters. We also needed to ensure, in collaboration with district health officials, that the COVID-19 vaccines were readily available in the four village clusters selected. Within each of the chosen quadruplets, we randomly selected one village for the placebo treatment; one for the standard health video; one for the low cash incentive video; and one for the high cash incentive video. This resulted in a total sample of 310 villages from the six different districts. Within each of the three treatment villages (health, low cash and high cash), 75% of the participants were randomly assigned to the village treatment, and 25% of the participants were randomly assigned to a placebo video. The complete list of villages and treatment assignments is available in the Enumerator IDs were assigned to village clusters. At the beginning of each enumeration day, enumerators downloaded their Qualtrics questionnaire assignments with the appropriate embedded videos. At the end of the day, these completed questionnaires were uploaded to the Candour server. No survey data were left resident on the individual tablets. Enumerators were provided with a random walk protocol for selecting households in each village; the detailed protocol was included in the pre-registration and is available at 10.7910/DVN/X5MBHP.Within each of the 310 villages, we randomly sampled 21 individuals. Households were randomly selected, and then, within households, we randomly selected individuals 18 years of age and older with the condition that they had not received the COVID-19 vaccine. There are four treatment arms with 80 clusters in each treatment arm. We sampled 5,900 in the first phase. The power calculations in our pre-registration assumed 300 villages in the design and at least 25 respondents per village. In this case, we are powered to detect an effect size of 0.06. All of the simulations—villages ranging in number from 200 to 400 with as few as 20 treated participants per village—were powered at 0.80 to detect an effect size of 0.12. We anticipated that our design, with four treatment arms, 312 villages and 21 treated participants per village, would be powered at approximately 0.80 to detect an effect size as small as 0.06.As part of phase III of the trial, we implemented a recruitment strategy for non-treated participants. For these non-treated participants, we collected information on their COVID-19 vaccination status as well as their demographics, their social network density and how and whether they learned about financial incentives or about getting the vaccination. We interviewed non-treated participants in all villages that were visited as part of phase III. The group of non-treated households within treated villages were selected by a similar random walk that was implemented in the initial treatment phase I.