Technical Appendix to NCHRP Report 571: Standardized Procedures for Personal Travel Surveys (2007) / Chapter Skim
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Pages 125-130
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From page 125... ...
119 CHAPTER 6 6. Pilot Surveys and Pretests 6.1 P-2: REQUIREMENTS FOR PRETESTS OR PILOT SURVEYS 6.1.1 Definition Pretests and pilot surveys are the process of testing various aspects of the survey design, protocol, instruments, analysis, etc.
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From page 126... ...
120 "If prior knowledge in these matters is not available a pilot or exploratory survey will be necessary. Even if there is adequate knowledge of the statistical properties of the material, pilot surveys are frequently advisable in large-scale surveys in order to test and improve field procedure and schedules, and to train field workers." (Yates, 1965, pp.48-49)
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From page 127... ...
121 A further type of preliminary test is a rolling pilot survey (Pratt, 2003)
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From page 128... ...
122 and use of pilot studies are sadly neglected in the survey literature." Further, they state "The same casual treatment that pilot survey design has received in the literature is also seen in the surveys themselves." However, having said this, and because Biemer and Lyberg are not writing about survey design, per se, they do not suggest what might be appropriate sample sizes. It seems likely that the sample sizes needed for true pretests – that is, the testing of a single element of a survey, such as a redesign of certain questions – would be able to be done effectively with a very small sample of households, such as 25 to 50 households.
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From page 129... ...
123 the pretest on 50 households would indicate that, with 95 percent confidence, the overall response rate would appear to lie between 4 percent and 34 percent. Supposing that the survey firm has performed the pretest in order to determine how many samples to draw for recruitment, and that a final sample of 3,500 households is required, then this result would define that the number of households that must be drawn in the sample would range between 10,300 and 87,500.
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From page 130... ...
124 20% ±3% 683 4 ±0.4 40 960 20% ±5% 246 4 ±0.8 40 240 20% ±8% 96 4 ±1 40 154 20% ±10% 61 4 ±1.5 40 68 30% ±3% 896 4 ±0.4 16 384 30% ±5% 323 4 ±0.8 16 96 30% ±8% 126 4 ±1 16 61 30% ±10% 81 4 ±1.5 16 27 To use Table 69, the following example is provided. Suppose a pilot survey is to be done in which it is desired to determine the response rate to within ±10 percent accuracy, where it is expected to be 40 percent, to determine the non-response rate to the income question to ±5 percent, when it is assumed that the level will be 20 percent, and to estimate the household trip rate, expected to be around 10 with a variance of 100, to within ±2 trips per household per day.
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