File:Car Brand Quality Ratings in 1980 by Infrequency of Trouble-Prone Models.png

English: Bar Graph of the 1980 Car Brand Quality Ratings by Infrequency of Trouble-Prone Models

This rating of the car brands is based on each brand's infrequency of trouble-prone models. The rating provides a measure of how well each brand'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 Some-Used-Car-Models-to-Avoid table and its reliability charts.

To form a car-brand quality measure from the 1980 list of Some Used Car Models To Avoid, the first step is to count each brand's entries on the list. Each model year of each model is treated as a separate entry.

Next, as the number of automobile models in a car brand varies greatly from brand to brand, it is necessary to take account of the fact that a brand 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 brand, as well as a variability in model data sufficiency, the number of a brand's entries in CR's 1980 Some-Used-Car-Models-To-Avoid list is divided by the total number of overall reliability ratings for the brand found in the reliability charts of the same issue of Consumer Reports. The overall reliability ratings are found in the Overall-Record 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 brand and is achieved only when a brand has no entry on the Used-Car-Models-To-Avoid list.

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

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

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# .