3.1. Choosing the method of data collection

When choosing the mode of data collection, a number of issues must be considered: effective coverage of target populations, data accuracy, potential bias of the survey sample, the survey mode(s), and the effort and cost of data collection (De Leeuw, 2008; Charrière and Neumann, 2010; Dahle, 2010; Hatjina et al., 2010; Mutinelli et al., 2010; Nguyen, Mignon et al., 2010). In a survey, the data can be collected by direct contact of an interviewer with the respondent (face-to-face interviews, telephone interviews) or the questions can be administered and answered by beekeepers without the assistance of an interviewer by means of a self-administered questionnaire (postal surveys, email surveys, internet surveys). The advantages and disadvantages of each mode are described in 3.2. Available data collection methods with advantages and disadvantages3.2. Available data collection methods with advantages and disadvantages3.2. Available data collection methods with advantages and disadvantagessection 3.2. Further references are given in the online supplementary material.