Sources of bias in mobile phone surveys in developing countries : a thesis presented in partial fulfilment of the requirements for the degree of Master of Applied Statistics at Massey University, Manawatu, New Zealand

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This study analyses three surveys carried out to measure food security in the poorest regions of Nepal: a baseline face-to-face (F2F) survey and two dual-mode surveys where respondents received either a F2F or a mobile phone interview. The goal of the analysis was to investigate whether mobile phone surveys could replace traditional F2F surveys without compromising the accuracy of data. Across all three surveys, households not owning mobile phones were found to be less food secure than households owning mobile phones: they consumed less food, had poorer diets and lower levels of food stocks. These findings reflected the results from analyses of demographic and socio-economic indicators which indicated that households not owning phones were poorer and less educated than households owning mobile phones. The mode of interview (mobile phone or F2F) was analysed for one survey. It appeared that responses about food security do not differ if given in a F2F interview or a mobile phone interview. In the two dual-mode surveys, non-response was analysed for those assigned a mobile phone interview. The results were contradictory: in one survey, mobile phone respondents were found to be more food-secure (also better educated and wealthier) than non-respondents while, in the other survey, they were found to be less food-secure (also poorer and less educated) than non-respondents. It is concluded that food security estimates from mobile phone surveys are biased with systematic differences between respondents of mobile phone surveys and the population. The overall bias is comprised of coverage bias and non-response bias. It is expected that coverage bias will decrease over time as mobile phone ownership increases, but that non-response bias will continue to affect food security estimates. Due to the contradictory results of the non-response analysis, it was not possible to consider bias correction techniques such as post-stratification. It was therefore concluded that reliable food security estimates cannot yet be obtained from mobile phone surveys in Nepal, and the continuation of dual-mode surveys was recommended.