HPMS Sample Management

1. HPMS Sample Management Highway Information Seminar Rosslyn, VA November 17, 2004

2. Importance of HPMS Sample • Sample used in lieu of complete data collection • Time & money saving process for providers • Expanded sample used to represent HPMS universe • Sample data used to: • Apportion funds to States • Measure fatality & injury rates • Estimate highway investment needs for Congress • Measure progress in congestion mitigation • Basis for highway fund authorization & budget levels

3. Why is sample management necessary? • Expanded sample used to represent HPMS universe • Road systems change over time • Traffic volumes change over time • Result: • Samples move among volume group strata • Impacts number of samples needed in each strata • Active sample management needed to maintain statistically valid sample

4. What can happen to samples? • The sample may become biased • The sample segments may become too short • The sample may become non-representative

5. How to manage the sample? • Perform regular sample reviews • Plot the samples on a State map • Check for clustering on the same facilities, within a county or district • Check for samples that are entirely on a structure • Review sampling procedures for bias

6. How to manage the sample? (cont’d) • Run the HPMS Submittal Software Adequacy Reports • check for unsampled volume groups • check for oversampled volume groups • check for undersampled volume groups • minimum 3 samples • maximum expansion factor of 100.000

9. Should see relatively low percentages.

13. Adjusting the Sample • Add/delete samples as needed • all eligible segments are in the volume group for selection • use random process to select/delete samples • Adjust sample in timely manner prior to the next submittal cycle

14. Useful Resources • HPMS CBT • “HPMS Sample Management” link: http://www.fhwa.dot.gov/ohpi/hpms/hpmspubs.htm • HPMS Field Manual • Contact: • Robert Rozycki– FHWA HQ • robert.rozycki@fhwa.dot.gov, Ph:202-366-5059