Table 3 Examples for sampling strategies used in studies

Without random sampling: “Present study was conducted in the southern Punjab i.e. Multan and Bahawalpur Divisions, the major cotton growing areas of Pakistan. The field study was limited to a manageable geographical area where female cotton pickers are living and have a great potential to be exposed to pesticides. The villages selected on the willingness of the female workers that participate in the study … After preliminary survey two female groups (13–35 years of age) were selected as cotton pickers and non-pickers (30–37 female in each group) from the selected area.” [162]

“Participants were recruited with the assistance of community leaders, churches, and local groups in the study area. Letters were sent to each of these entities which contained a clear explanation of reasons for the study, study objectives, inclusion criteria, consent to participate, and voluntary participation. These leaders and groups made announcements to the general public or community gatherings for a month. Those farmers who expressed interest in participation were invited to meet at the community leaders’ residence, group meeting locations, or church premises. At these meetings, the principal investigator reviewed the study and explained the content. If the farmer wished to participate, the consent form was signed, and the questionnaire was given to complete.” [163]

With random sampling: “From a universe of approximately 3500 subjects, a random sample of about 1100 workers directly exposed to pesticides was performed, considering as such those subjects who mix/load and/or apply pesticides.… As mentioned, applicators are professional workers authorized by the Agriculture, Livestock and Food Ministry to perform their tasks. They usually work in several extensive crops in the same area of the province, as independent professionals (the owners of the machinery) or as employees of an agrarian company.” [46]

“The 2005 and 2006 surveys were conducted by a market research company and included 6359 users in 24 countries … Approximately, 250 users were sampled from each country. In each country, a local market research team identified regions where the use of pesticides was moderate to intensive… The selection of respondents was on the basis of quota sampling and targeted users on smallholdings of below average size and contract spray operators in countries where there were significant numbers of such users. The local market research teams designed their target smallholder farmers in terms of farm size and typical crops grown. Screening questions were used to ensure that the sample satisfied the quota requirements.” [169]

“The target population of this survey included male farmers residing in rural areas in South Korea. The sampling frame for this survey was constructed by use of 2010 Korean Agricultural Household Registry data. Primary sampling units were formed out of the local administrative districts. We stratified primary sampling units into three strata based on three variables, which were the number of farm households, the farm household population by age group (< 15, 15–65, > 65) and the proportion of households residing in apartments. The selection of a 3% limit of error in the estimate yielded a needed sample size of roughly 2000. A total of 197 primary sampling units were selected by probability proportional to size sampling method. In the final sampling stage, the sample size in a primary sampling unit was 10. Trained interviewers visited each selected household and explained about the study.” [96]