A natural break in the responses occurred after the first-wave mailing. Non-response bias was assessed by comparing those responses received after the first-wave mailing but before the second-wave mailing early respondents with the combined responses received after the second- and third-wave mailings . late respondents . The results from a multivariate T-test, computed using the key study variables, suggest that early respondents do not display statistically significant differences from late respondents ps . 0.3613