Is there any certain limit to the product that you are going to test? the answer is yes, ideally is 2 products so the respondents will easily evaluate which one they like A or B. In determining the maximum number to be tested by the respondent, we should consider respondent's ability to evaluate the product and how they use the product.
Unfortunately we don't live in the 'ideal world' so usually the marketing want to ask help from respondents in determining the products. so most of the time we have to test 3 products and yes I might say the 3 is the maximum number of product that respondent can evaluate fairly. How about if there are more than 3 products to be tested, say 4 or more. We know that respondent will have difficulty in evaluating more than 3 products. In this situation, researcher will apply what we call as round robbin design. Respondent will only try 3 products, but in the analysis we will compare 4 products or more. So we will depend on the statistical analysis for the result.
How to place the product should also be considered, we can place the product monadically (product is placed one by one). In this case we ask the respondent to evaluate first product, then ask the evaluation, then place the second product, then do evaluation on the second product. Using this way, it is a little bit difficult in getting the comparison. We may place 2 product at the same time and ask the respondent to compare directly. In field, comparing 2 product directly sometimes difficult to administered.
