5.1. Non-response bias
As with similar studies using a dyadic methodology, the response rate from buyers is quite low. Non-response bias occurs when the opinions and perceptions of the survey respondents do not accurately represent the overall sample to whom the survey has been sent. One test for non-response bias is to compare the answers of early vs. late responŽ. dents to the survey Lambert and Harrington, 1990 . The idea is that late respondents are more likely to answer the questionnaire like non-respondents than Ž are early respondents Armstrong and Overton, . 1977