The sample for the survey was selected using stratified random sampling, broadly following similar methodology explained in the ES Sampling Note. However, unlike ES that uses three levels of stratification (size, location, and sector), this survey uses two levels of stratification, namely location/region of the informal busines and the gender of the main business owner.
Stratifies random sampling was preferred over simple random sampling for several reasons:
a. To obtain unbiased estimates for different subdivisions of the population with some known level of precision
b. To obtain unbiased estimates for the whole population. The whole population, or universe of the study, is informal sector businesses operating in Zimbabwe. Informality is defined as any business that doesn't have registration from Zimbabwe Registrar of Companies.
c. To make sure that the final total sample includes establishments from different regions and from businesses owned by male and femal.
d. To exploit the benefits of stratifies sampling where population estimates, in most cases, will be more precise than using a simple random sampling method (i.e. lower standard errors, other things being equal.)
e. Stratification may produce a smaller bound on the error of estimation than would be produced by a simple random sample of the same size. This result is particularly true if measurements within strata are homogeneous.
f. The cost per observation in the survey may be reduced by stratification of the population elements into convenient groupings.
Total sample target: 1020
