1. Impacts of Proxy Reporting in Household Surveys on Trip Rates
Ed Hard | David Pearson
13th TRB Transportation Planning Applications Conference
Reno, NV
May 12, 2011

2. What We Did….
Analyzed difference in the number of trips reported by respondent, proxy, and diary
Used data from 3 HH surveys
All surveys used same methodology and instruments
Person trips compared and evaluated by retrieval method

3. Evaluation of Person Trips
Compiled and compared for respondent, proxy, and diary methods by
Aggregate totals by urban area
Per person by age cohort
Per person by HH size and income
Various categories of person and HH lifecycles
HBW, HBNW, NHB by area and by age cohort, HH size and income, and lifecycle

4. Comparison of Person Trip Rates
Calculated difference in rates to determine if statistically significant difference between
Respondent and proxy
Respondent and diary
Proxy and diary
Used test statistic

5. Summary of Findings
Person trip rates for respondent 25 to 45 % higher than proxy; for diary 58-95% higher than proxy
When stratified by age cohorts, rates for respondent and diary consistently higher than proxy
No significant difference in male vs. female rates
Significant under-reporting of adults represented by proxy

6. Comparison of Trip Rates by Retrieval Method
RIO GRANDE VALLEY
Comparison of Trip Rates by Retrieval Method
AUSTIN
AMARILLO

7. Summary of Findings
Appears to be a tendency to over-report HBW trips and under-report HBNW and NHB
Potential impact of this on TDMs and estimates of total travel is significant
Trip rates essentially the same for the three areas for each method of data retrieval
Implies raw survey data may be combined between urban areas and weighted to represent local conditions
Analysis of Houston HH survey data reveals same general findings on person trip rates in relation to retrieval method

8. Comparison of Trip Rates by Purpose by Retrieval Method
Results/Trends Similar for All Areas
RIO GRANDE VALLEY
RIO GRANDE VALLEY
RIO GRANDE VALLEY

9. Recommendations For Texas Travel Survey Program
Allow no more than 20 percent of individuals over age 15 to be represented by proxy
Modify HH survey analyses to include development of adjustment rates by age cohort and purpose for proxy individuals
Research to examine combining unweighted HH surveys from different areas to develop trip rates for areas without HH surveys

10. QUESTIONS Ed Hard (979) 845-8539 e-hard@tamu.edu David Pearson
(979)