Note that I say Interim View and not Interim Analysis
At several points during the survey, together with checking the number of responses obtained, the questionnaires already entered and verified should be crosstabulated for the variables that describe the sample, stratification or grouping variables. Are we obtaining the balanced sample that we intended?. Are the number per strata as we forecasted they will be?
Changes in advertising or promotion must be indicated if we are not getting the level of response expected.