Before revision: when respondents misunderstand a question, or find it difficult to answer Processing error: mistakes in data coding Non-response or Participation bias: failure to obtain complete data from all selected individuals After sampling, a review should be held of the exact process followed in sampling, rather than that intended, in order to study any effects that any divergences might have on subsequent analysis.
After revision: when respondents misunderstand a question, or find it difficult to answer Processing error: mistakes in data coding Non-response or Participation bias: failure to obtain complete data from all selected individuals After sampling, a review is held of the exact process followed in sampling, rather than that intended, in order to study any effects that any divergences might have on subsequent analysis.