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HPMS Sample Management
Highway Information Seminar in Rosslyn, VA
November 17, 2004
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: a) Apportion funds to States b) Measure fatality & injury rates c) Estimate highway investment needs for Congress d) Measure progress in congestion mitigation e) Basis for highway fund authorization & budget levels
Why is sample management necessary?
- Expanded sample used to represent HPMS universe
- Road systems change over time
- Traffic volumes change over time
- Results: 1) Samples move among volume group strata, 2) Impacts number of samples needed in each strata, 3) Active sample management needed to maintain statistically valid sample
What can happen to samples?
- The sample may become biased
- The sample segments may become too short
- The sample may become non-representative
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
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
Adjusting the Sample
- Add/delete samples as needed a) all eligible segments are in the volume group for selection b) use random process to select/delete samples
- Adjust sample in timely manner prior to the next submittal cycle
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