Table 2

Qualitative sampling approach by informant category

Informant category		Purposive criteria
Local government area health officials (LGAs)	Positive deviants (PD)	At least one state per geographical zone represented in the final LGA sample, for geographical representativeness across Nigeria Prioritise states with the highest number of COVID-19 cases reported to Nigeria Centre for Disease Control in each zone Balance of urban and rural geographies Exclude areas with known security concerns for in-person data collection
Local government area health officials (LGAs)	Comparators	Not eligible to be a positive deviant Similar geography (urban or rural) as the PD (usually geographic neighbour) Similar relative wealth as the PD Within the same state as the PD Exclude areas with known security concerns for in-person data collection
Primary health care facility (PHC) officers in charge	PDs	If no clear PHC facility-level pattern emerged in the quantitative analysis, PHC facilities were randomly selected from a list generated by LGA officials.
Primary health care facility (PHC) officers in charge	Comparators	Randomly selected from an available facility list of non-positive deviants
Opinion leaders	Both positive deviants and comparators	LGA and facility informants were asked to identify additional informants critical to the local COVID-19 response A list was generated of these suggestions and relevance of suggestions confirmed. Individuals were randomly sampled from the final list