English: Bar Graph of the 2005 Car Manufacturer Quality Ratings by Infrequency of Trouble-Prone Models

This rating and ranking of the car makers is based on each manufacturer's infrequency of trouble-prone models. The rating provides a measure of how well each manufacturer's models successfully avoided the bottom end of the model-quality spectrum.

The formation of this measure of quality is based on two sections of Consumer Reports - its Used-Cars-to-Avoid table and its reliability charts.

To form a car-manufacturer quality measure from the 2005 list of Used Cars to Avoid, the first step is to count each manufacturer's entries on the list. Each model year of each model is treated as a separate entry.

Next, as the number of automobile models sold by a car manufacturer varies greatly from company to company, it is necessary to take account of the fact that a manufacturer with more models has a greater opportunity to have more model years of low quality. To compensate for a possibly inflated, or deflated, frequency of trouble-prone model years of a manufacturer, as well as a variability in model data sufficiency, the number of a manufacturer's entries in CR's 2005 Used-Cars-to-Avoid list is divided by the total number of overall reliability ratings for the manufacturer found in the reliability charts of the same issue of Consumer Reports. The overall reliability ratings are found in the Reliability-Verdict row of the 1980 reliability charts.

By the method of computation, this quality measure begins with 0 and may run to a value some greater than 1. The value of 0 is the highest quality rating attainable by a car manufacturer and is achieved only when a manufacturer has no entry on the Used-Cars-to-Avoid list.

The quality ratings of the car manufacturers by this set of computations are given in the bar graph above. Only those manufacturers with at least 5 overall CR reliability ratings are included.

When two or more manufacturers have no entry on the list of Some Used Car Models to Avoid, a manufacturer with a greater number of reliability ratings appears before a manufacturer with a lesser number of reliability ratings.

For the 1975, 1980, 1985, 1990, 1995, 2000, 2005, and 2005 charts providing the automobile-manufacturer quality ratings and rankings by overall reliability and infrequency of trouble-prone models, Saab, Volvo, and Jaguar are treated as independent companies.

For a Google Knol that summarizes the changes in car brand and manufacturer ranking by this quality measure from 1990 to 2010, visit http://knol.google.com/k/james-bleeker/automobile-quality-by-car-brand-and/3o3u27f0whd6k/2?hd=ns# .