Problems with good sampling methods

• Nonresponse: People who feel they have something to hide or who don’t like their privacy being invaded probably won’t answer. Yet they are part of the population.
• Response bias: Fancy term for lying when you think you should not tell the truth, or forgetting. This is particularly important when the questions are very personal (e.g., “How much do you drink?”) or related to the past.
• Wording effects: Questions prompt you to give a particular response.