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Procedures and Measures for Further Research 51 needed on whether to survey these persons or whether some group quarters should be included and others not. It is recommended that research be conducted on these issues using existing surveys for analy- sis. By examining a survey for which there is no minimum age, the data obtained on children under 5 years of age could be compared with data from adults in the same household. From this, it would be possible to determine the extent to which the infant's data could have been inferred from the parents' data. It would also be useful to determine whether trip rates and other related informa- tion are ever corrected for infants when analyzing those data sets that did not include infants in the collection of travel data because this may have significant impact on mode-choice and automobile occupancy. Parents with infants are often restricted to using an automobile available to the house- hold, and this decreases the potential for transit use. Failure to include infants will result in incor- rectly lower average automobile occupancy rates that will probably not match occupancy rates from other sources. It is also recommended that analyses be done on surveys that include persons from group quar- ters. Specifically, it is suggested that level of tripmaking be compared between persons living and not living in group quarters. It would also be worthwhile to look at what fraction of total trips are represented by people living in group quarters (through examining census data) to determine the effect of inclusion or exclusion on overall regional travel statistics. It is anticipated that standard- ized procedures would suggest specific conditions that need to be met to warrant the inclusion of group quarters in surveys. These might include situations in which the retired elderly people exceed a certain fraction of the population of the study region or where there might be a military or other mobile institutional presence (e.g., colleges or universities with dormitory accommodations) in excess of some proportion of total population. 4.2.2 D-9: Times of Day for Contacts Within telephone surveys, the time of day when contact is attempted has a critical influence on response rates. There is a wide range of practices in existing surveys, however, and these have never been formally documented. In some surveys, the client agency may stipulate the hours between which telephone contacts can be made by the contract firm. Because different cities show markedly different habits with respect to work times and times at which people retire for the night, this may not be an area in which consistency of practice will be possible. It may be possible, however, to spec- ify a core period of time when calling would normally be productive and to specify other times when calling is almost certainly not productive. For example, calling is generally productive between 6 and 8:30 P.M. on weekday evenings. It is recommended that recent surveys be reviewed to determine what has been set as appropriate times. By examining call attempts and outcomes in call histories, it would be possible to determine the relative productivity of calls made at different times of the day. Particular attention should be paid to determining the most productive and acceptable hours for calling on weekends. A second issue that needs to be addressed in this area is how to determine when to re-contact households that have either requested a non-specific call-back or are considered to be soft refusals. It seems possible that some consistent rules can be established on how to distribute times for call- backs to try to resolve previously incomplete surveys. There appears to be a lack of common prac- tice on when to make a subsequent attempt after finding the number is busy, there is no answer, or an answering machine picks up the call. In some instances, the protocol appears to be to recall the household at least once, and sometimes more than once, on the same evening as the initial call. In other cases, the call may be re-rostered for the same time on the next day or the same time in the next week. By reviewing procedures that have been used in prior surveys and also those that may be used in other areas of market research, it may be possible to recommend guidelines for re-contacting sample units.