Answer: C. Unreliable or the value on the variable had changed
Explanation: Professor Myth's variable which in this case are the respondents could have changed. There is every possibility that, after a year, when he wanted to repeat the application, respondents who were not divorced during the first data collection were now divorced. Therefore a change in view of the variable. It is also possible that the data from the respondent was unreliable which could occur when respondent do not want to disclose their status or do not understand the importance of the information being asked such that they provide different response to the same question being asked. The information provided by such respondent would be unreliable and inadvertently affect the conclusion
