Match each research technique to the question it answers best.

• Probability survey → How common something is across a whole population
• In-depth interview → How people themselves account for what they do
• Ethnography → What happens in a setting, as against what is reported about it
• Documentary and secondary analysis → How a pattern has changed across decades already recorded

The list is not a hierarchy. Each technique is strong exactly where another is weak, which is why mixed designs are common: a survey establishes how widespread something is and interviews establish what those doing it take themselves to be doing, and neither substitutes for the other.