Estimate time to fill a survey.
Survey length is driven by open-ended questions. A closed question takes seconds, while a free-text response takes over a minute of typing and thought, so six open questions can outweigh twenty-six closed ones. Adding a fixed half minute for the landing page and consent gives a completion estimate, and completion time is the single best predictor of dropout.
Completion time
Total seconds = closed questions x seconds each + open questions x seconds each + 30 seconds intro
Dropout bands
Under 5 minutes low risk, 5 to 10 moderate, 10 to 20 high, above 20 very high
Under ten minutes for general audiences and under five for cold recruitment. Dropout rises steeply with length, and abandoned responses are usually unusable.
Cut open questions first, since they cost the most time per item and are the hardest to analyse. Replacing them with a well-designed closed question often loses little.