Laban, thank you for your comment. (It's been a long time since we worked together in Busia!) Within a given questionnaire, people refer to "respondent fatigue" and the subsequent effect on quality as "fatigue bias" to capture the fact that people give quicker and less thoughtful or accurate answers as surveys go forward. I think the same term would apply across surveys. I have seen it measured within surveys but not across surveys (although in heavily surveyed areas, one certainly hears anecdotes to this effect). One survey of this work, for a particular kind of survey, is here: http://www.sciencedirect.com/science/article/pii/S0965856411001777.