Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 24
24 Standardized Procedures for Personal Travel Surveys
instrument, sampling, etc. During the design phase, several sequential pretests could be
conducted to test various refinements of the instrument, protocol, sampling, etc.
Second, it is recommended that one or more pretests and/or one or more pilot surveys should
be an essential step in all transportation surveys unless there are specific circumstances that ren-
der such a step unnecessary and unlikely to produce useful information.
It is further recommended that the following guidelines with respect to pilot tests and pretests
be adopted:
1. In any survey in which interviewers will interact with respondents, the pilot survey or
pretest should include listening in to interviewers to determine how they interact with
potential respondents, how well they keep to the script of the survey, and whether the script
causes difficulties in conversational style.
2. In any survey that uses interviewers or observers, there should be a debriefing with those
used in the pilot survey or pretest to determine whether difficulties were experienced in
handling survey procedures, questionnaires or other materials, scripts, etc.
3. If it has been 10 years or more since the last time a survey was done, a pilot survey should
always be undertaken because the changes in population that will have occurred will ren-
der any past experience irrelevant.
2.3.2 P-3: Sample Sizes for Pretests and Pilot Surveys
Because we recommend that pretests and/or pilot surveys be conducted in all future travel sur-
veys, it is appropriate to establish the required sample size of these initial tests or surveys. For
further discussion, the reader is referred to Section 6.2 of the Technical Appendix.
It is recommended that the following standardized procedures be adopted by the profession:
1. Whenever possible, the main sample should be drawn first and the pilot survey or pretest sam-
ple drawn only from those households or persons who were not drawn for the main sample.
When the pilot survey or pretest is being conducted to determine the sample size required
for the main survey, two options are possible. The first option is that a main sample can be
drawn that is expected to be more than sufficient in size. The pilot survey or pretest sam-
ple can then still be drawn subsequently from those households or persons who will not be
included in the main sample under any likely circumstances. The second option is to draw
the pilot survey or pretest sample at random from the total population and then be sure to
exclude all such drawings from the population for drawing the main sample. The former
of these two is the preferred method.
2. No pretest or pilot survey should use a sample of less than 30 completed households or respon-
dents. Exercises using smaller samples than this should be regarded as preliminary tests and
pre-pilot surveys and should always be followed by a pretest or pilot survey with at least a
30 respondent sample size.
3. The minimum sample sizes shown in Table 6 should be used in all pilot surveys and appropri-
ate pretests.
2.4 Survey Implementation
2.4.1 E-2: Ethics
Ethics describe minimum acceptable standards of conduct or practice. In travel surveys, this
relates to how a survey agency conducts itself with respect to those interviewed, the client, any
subcontractors, and the public as a whole. It also relates to a survey agency's actions following
the data collection process when data are cleaned, coded, analyzed, and archived.
OCR for page 25
Summary of Recommended Standardized Procedures and Guidelines 25
Table 6. Sample sizes required for specified levels of accuracy.
Measure Assumed Desired Sample Measure Assumed Desired Assumed Sample
Value Accuracy Size Value Accuracy Variance Size
Response Rate 50% ±5% 384 Household or 10 ±1 100 384
50% ±10% 96 Person Trip Rate 10 ±2 100 96
50% ±15% 43 10 ±3 100 43
50% ±20% 24 10 ±4 100 24
60% or 40% ±5% 369 10 ±1 50 192
60% or 40% ±10% 92 10 ±2 50 48
60% or 40% ±15% 41 10 ±3 50 21
60% or 40% ±20% 23 10 ±4 50 12
75% or 25% ±5% 288 7 ±0.5 70 1076
75% or 25% ±10% 72 7 ±1 70 269
75% or 25% ±15% 32 7 ±1.5 70 120
75% or 25% ±20% 18 7 ±2 70 67
Non-response 10% ±3% 384 7 ±0.5 50 768
to a Question 10% ±5% 138 7 ±1 50 192
10% ±8% 54 7 ±1.5 50 85
10% ±10% 35 7 ±2 50 48
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
Ethics reflect what all stakeholders may consider "fair" or "reasonable" conduct by those involved.
In practical terms, the application of ethics involves implementation of precautions to protect those
affected from adverse effects. Ethics protect the rights of individuals and groups and serve to
reduce public disapproval and criticism of what is done. A review of the ethics standards used in
various other areas of surveying is provided in Sections 2.2.2 and 7.1 of the Technical Appendix.
After reviewing documents prepared by various associations on different aspects of ethical
conduct in the execution of travel surveys, it is recommended that the following ethical conduct
be observed in all future travel surveys:
1. The anonymity of the persons surveyed, and the confidentiality of the information they
provide, must be protected at all times;
2. A survey respondent may not be sold anything or asked for money as part of the survey;
3. Persons must be contacted at reasonable times to participate in the survey and must be
allowed to reschedule participation in the survey to a different time if that is more con-
venient for them;
4. Survey personnel must be prepared to divulge their own name, the identity of the research
company they represent, the identity of the agency that commissioned the study, and the
nature of the survey being conducted, if requested by a respondent;
5. Children under the age of 15 may not be interviewed without the consent of a parent or
responsible adult;
6. A respondent's decision to refuse participation in a survey, not answer specific questions
in the survey, or terminate an interview while in progress must be respected if that is the
respondents' firm decision;
7. Respondents may not be surveyed or observed without their knowledge: methods of data
collection such as the use of hidden tape recorders, cameras, one-way mirrors, or invisible
identifiers on mail questionnaires may only be used in a survey if the method has been fully
disclosed to the respondent and the respondent agrees to its use.
