A considerable strength of the WMHS initiative is that the population survey research approach generally has been held constant. Each respondent has been sampled via advanced population survey methods, has been presented with the same type of survey introduction, and has completed a highly structured and standardised field survey interview assessment using the same questions in each country, in accord with standardised translations. One exception to this was France, whose sampling frame only included households that had a telephone, although interviewing itself was conducted face-to-face.
