A glance at several national surveys reveals a large number of questions that ask respondents about the time of an event. For example, the National Crime Survey asks Question (1) for each crime victimization that the respondent reports:

1. (1) In what month did (this/the first) incident happen? (Show calendar if necessary. Encourage respondent to give exact month.) [NCS]

We presented similar questions in Chapter 3. Equally common are questions, such as (2), concerning the duration of a state or event:

1. (2) How much time did you lose because of injuries? [NCS]

These probes for a time point or duration, common as they are, aren't the only questions that require respondents to consider when or how long ago events occurred. Many survey items specify a reference period and ask whether or not an event of a given type occurred within it, or they specify a duration and ask whether an event or state lasted for a longer or shorter time. In answering Questions (3) and (4), for example, a respondent doesn't have to supply a date or duration but must still determine the time of the occurrence or the length of time:

1. (3) Did the accident happen during the past 2 years or before that time? [HIS]

2. (4) IF RETIRED, IN SCHOOL, KEEPING HOUSE, OR OTHER: Did you ever work for as long as one year? [GSS]