For most survey questionnaire forms (especially those administered by an interviewer) questions are not asked in a strictly linear fashion. For example, if the response to same question is "YES", the interview will follow it with a question different from that were the response "NO". If the questions on a survey form are numbered sequentially, Q1, Q2,... ,QN, then one fully completed response form might look Ql-Q5-Q7-Q12-Q50 and another might look like Ql-Q8-Q12-Q39-Q50 where N=5D. The remaining questions in each case are not missing in the usual sense of missing data, but were not asked and are "not applicable" based on the responses provided at an earlier stage and on the underlying structure of the questionnaire. These diverse patterns of response and interrogation are frequently referred to as skip patterns.