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42 Standardized Procedures for Personal Travel Surveys 2. Coverage error should be estimated as the percentage deviation of the population of the study area estimated using the planned sample, from that of the population of the same area using a reliable external source. That is, coverage error must be estimated using the definition of coverage error in Equation 3 above. 3. Each future survey should include descriptions of the survey population and the sampling frame, and coverage error should be reported. 2.7.4 Q-5: Proxy Reporting as a Quality Indicator Proxy reporting in a travel survey is the reporting of one person on behalf of another, as dis- cussed in Section 2.2.2 of this report. While proxy reporting is unavoidable in some cases, it is also susceptible to survey design and the method of survey execution. Because proxy reporting affects the accuracy of the data, it is reasonable to suggest that more proxy reporting is likely to lead to less accuracy in the data. Accuracy is an important compo- nent of data quality and, therefore, it is suggested that the incidence of proxy reporting can be used as a measure of data quality of the data set. This is addressed in more detail in Section 10.4 of the Technical Appendix. It is recommended as a standardized procedure that 1. Each travel survey should include questions on the age of each person in the household (see also Section 2.1.1) as well as the capability of each member over the age of 14 to complete the survey. 2. Only those individuals 15 years of age or older and those capable of completing the survey should be included in estimating the level of proxy reporting in the data. 3. For each individual in the household, it should be established whether the information being reported for that individual was Prepared by the individual and Reported by the individual. 4. Each travel survey should report the percentage of proxy reports in the data based on the above conditions relating to what represents a proxy report for this purpose. 2.7.5 Q-6: Validation Statistics Validation is the process of verifying the authenticity of collected data by recontacting a sam- ple of households. It is used in interview-based surveys to determine whether the interviewer actually conducted the interview and whether the information obtained is accurate. It can also be used in self-administered questionnaires where the validation survey then usually involves a face-to-face or telephone interview to check the quality and completeness of data. Validation surveys typically involve a limited set of key questions only. These usually include identifying and trying to make contact with the person involved in the original sur- vey and verifying a few trips reported by the respondent. Validation surveys are conducted to ensure the authenticity and integrity of the data. Further discussion is provided in Section 10.5 of the Technical Appendix. The following recommendations are proposed with respect to validation surveys: 1. Each travel survey should conduct a validation survey. 2. The validation survey should use the following three questions: Question 1: Did you complete the initial survey? (yes or no) If "yes," go to Question 3 below. If "no," go to the second question below.