DOI: 10.6077/j5/ch1qph
title: General Estimates System (GES), 1995

description: &lt;p&gt;Data for General Estimates System (GES) come from a nationally representative sample of police-reported motor vehicle crashes of all types, from minor to fatal. The system began in 1988, and was created to identify traffic safety problem areas, provide a basis for regulatory and consumer intiatives, and form the basis for cost and beneift analyses of traffic safety initiatives. The information is used to estimate how many motor vehicle crashes of different kinds take place, and what happens when they occur. In order for a crash to be eligible for the GES sample, a police accident report (PAR) must be completed, it must involve at least one motor vehicle traveling on a traffic way, and the result must be property damage, injury, or death. GES samples approximately 50,000 PARs each year.&lt;/p&gt;
description: General Estimates System
description: collection_notes: The police accident reports (PARs) from which GES data are coded are a probability sample of police-reported crashes that occurred in the United States. Since each crash that occurred in the survey year had a chance of being selected, the design makes it possible to compute not only national estimates but also probable errors associated with the estimates. The selection of the sample of PARs for the GES was accomplished in three stages. The first stage is a sample of geographic areas, called Primary Sampling Units (PSUs), from across the United States. A PSU is either a central city, a county surrounding a central city, an entire county, or a group of contiguous counties. The U.S. was divided into 1,195 of these PSUs. The PSUs were then grouped into 12 categories according to the following geographic regions and types of PSUs:' Geographic Region: Northeast, South, Central, and West' Type: Large Central City, Large Suburban Area, and All others.

 The second stage of the design is a sample of police jurisdictions within the geographic areas. In most areas, the number of police jurisdictions is more than can reasonably be visited by a data collector. All jurisdictions within a PSU were enumerated and the number of crashes investigated by each was determined. A probability sample of jurisdictions within each PSU was selected with probability proportional to the number of crashes investigated, i.e., as the number of crashes investigated increased, the probability of selecting that jurisdiction increased. An average of six or seven police jurisdictions were selected within each area.

The third and final stage is the selection of PARs within the sampled police jurisdictions. The PARs are grouped, or stratified, into one of four groups by the data collector: ' Group 1: All crashes involving a towed passenger vehicle, i.e., a passenger car, sport utility vehicle, pickup truck or van, but no medium or heavy trucks;' Group 2: All crashes involving a medium or heavy truck and where at least one passenger vehicle was towed or an involved person was injured; ' Group 3: All crashes not involving a towed passenger vehicle or medium or heavy truck, but one in which an involved person was injured; and, ' Group 4: All other crashes. Within each of these groups a systematic sample of crashes is selected, based on different sampling ratios. In some very large police jurisdictions the number of police investigated crashes is too many for reasonable listing. In these jurisdictions the data collector will list a subsample of PARs, with those listed depending on the PAR number. The data collector obtains copies of the selected PARs and sends them to the NASS zone centers for quality review and processing. The zone center forwards the selected PARs to the data processing contractor, who extracts the required data, codes it into a common format, and creates an electronic file. In 1997 approximately 55,000 PARs were sampled and coded.