Suppose you are sending out questionnaires to a randomly selected sample of 100 managers. The frame for this study is the membership list of the American Managers Association. The questionnaire contains demographic questions about the company and its top manager. In addition, it asks questions about the manager’s leadership style. Research assistants are to score and enter the responses into the computer as soon as they are received. You are to conduct a statistical analysis of the data. Name and describe four non-sampling errors that could occur in this study.