Before designing your test you have to be aware of following:
Test persons will never answer you correct.
- Some persons will answer socially correct to the answers but not in reality. Some are overcoming this problem by asking what the test person thinks the neighbours will do.
- If you are asking a question in another situation you will get another answer. If you ask about the shopping for the dinner after the dinner or in the morning you will not have the stress the consumer have ˝-1 hour before dinnertime.
Make the interviews as near in both time and place to the real purchasing situation. The best position will be in the supermarket as near to the product department as possible and as late afternoon as possible for daily-products.
Test persons do not have time for very long interviews. You must limit your questions to interviews at about 10-15 min. Another important matter is the number of completed interviews you need in order to get statistical sufficient data. A general rule will be to have min. 150 completed interviews plus extra 50 for each new design you are adding over 3 designs. In order to get 150 completed interviews you need to stop about 300 persons and use about ˝ hour on each completed interview.