The National Longitudinal Study of the High School Class of 1972 (NLS) employs a combination of mail, telephone, and personal interview data-gathering techniques. The NLS quality control process begins with editing each returned questionnaire to determine if certain key items are answered and if responses are consistent. If the respondent failed to properly answer these key items, the questionnaire fails edit and the respondent is contacted by telephone. The purpose of this study was to determine why so many NLS questionnaires fail edit (over 60 percent of the third follow-up survey). Five general conclusions should be emphasized: (1) though subgroup differences were found, their magnitude is too small for concrete recommendations for survey practice; (2) the majority of edit failure problems associated with itemized financial questions revolve around the respondents' failure to supply answers to each of the requested line items; (3) items structured as "check all responses that apply" are likely to be failed by a substantial number of respondents; (4) reflexive items have a realizable potential for reducinq respondent burden where repetitive information is required; and (5) overall data entry errors were low except for items requiring itemized financial information. (Author/BW)