You may want to keep in mind that bias can be created by:
- Having a subliminal message in your question: i.e. How much do you like vegetarian meat alternatives? This type question contains the subliminal message, that the respondent is supposed to like vegetarian meat alternatives. Instead ask: What do you think of vegetarian meat alternatives?
- Answers that are skewed towards one direction. If you go from 'like very much' to 'like just a little bit', leaving out neutral or disapproving answers, your questionnaire won't work. So make sure to use the Likert scale which contains all options from 'like very much' via 'neither like nor dislike' to 'dislike very much'.
- Feelings of guilt or other negative emotions. People tend to demonstrate socially approved behaviour rather than telling the truth if there is a negative emotion or social judgement attached to it.
If you research delicate subjects it is best to use masked questions i.e: How much alcohol a week would you consider to be harmless to your health?
Another way of asking delicate questions is to use agree or disagree statements in the question i.e: I don't mind how animals are treated as long as I can afford to buy meat: Then use 1-5: totally agree, agree, neither agree nor disagree, disagree, totally disagree.