Wave

Within the context of survey research, a wave refers to each separate survey in a series of related surveys. If a survey is conducted only once, then the concept of a "wave" does not apply. It is when a survey is conducted two or more times, for example, once a year for 5 years in a row, that each repeated survey is called a wave. These waves may represent a panel survey in which the same respondents are tracked over time, often being asked some or all of the same questions in each wave. Other multi-wave (longitudinal) surveys use independent samples at each wave.

When a panel study is conducted and respondents who are interviewed in a prior wave are not successfully interviewed in a subsequent wave, even though they should have been, then panel attrition results. Common reasons for panel attrition at subsequent survey waves are refusals, moving, and illness or death. Some long-term survey designs rotate respondents in and out of being interviewed at various waves. Other long-term designs eliminate a random portion of the respondents that had been interviewed in previous waves and replace them with a random sample of "first time" respondents who likely will be contacted again in future waves.