Toyota Age Equivalents
by James Bleeker

The following table provides the estimated ages of when a typical 1999 model by Toyota Motor Corporation will be about as troublesome as a typical 1999 model of selected other manufacturers and lines were at ages 3, 4, 5, 6, and 7 years.

The computation of these estimated age equivalents is rather involved. (While some PhD theses seem to have been thrown together in a Saturday afternoon, the above estimates were not, as you'll soon see.)

What follows is, in the main, what appeared in a November 2007 article on AutoOnInfo.net.

We begin with the following table of Reliability Score averages for model year 1999.

Next, we plot the Reliability Score averages of Toyota Motor Corporation for each of the above age ranges (2-to-4 years, 3-to-5 years, ..., 4-to-6 years) and make an extrapolation of these plots, a linear regression of degree one. We will first determine an estimate of when a typical 1999 model of Toyota Motor Corporation will be as troublesome as a typical 1999 model of General Motors Corporation at about age 3 years. To do this, we plot GM's Reliability Score average for the first age range (2-to-4 years) and draw a horizontal line. For the x-axis, we use the midpoint of each age range. We have:

The equation on the chart is the regression equation for Toyota's extrapolation. From the chart's extrapolation, we see the estimate of when a typical 1999 Toyota model may be as troublesome as a typical 1999 GM model circa age 3 years to be about 19 years. By computation, substituting GM's rounded Reliability Score average of .27 (for age range 2-to-4 years) for y in Toyota's regression equation, we obtain an estimate of 19.0 years. Another way of viewing the result is: If a typical 1999 GM vehicle became unacceptable to own by reason of trouble or risk of trouble at about 3 years old (calendar year 2002 or earlier), then a typical 1999 Toyota vehicle may become unacceptable to own at about age 19.0 years, or circa calendar year 2018.

The next four charts depict similarly derived estimates of age equivalents (with respect to vehicular deterioration) for a typical 1999 model of Toyota corresponding to approximate ages 4 years, 5 years, 6 years, and 7 years of a typical 1999 GM model.

From the charts, we see that the estimates of when a typical 1999 Toyota model may be as troublesome as a typical 1999 GM model at about ages 4 years, 5 years, 6 years, and 7 years are about 22 years, 25 years, 29 years, and 33 years, respectively. By computation, substituting GM's rounded Reliability Score averages for y in Toyota's regression equation, we obtain the following estimates of when a typical 1999 Toyota model will be as troublesome as a typical 1999 GM model at ages 4 years, 5 years, 6 years, and 7 years: 22.4 years, 25.5 years, 29.4 years, and 33.1 years, respectively.

Note that each succeeding chart requires an extrapolation farther into the future and consequently each succeeding age-equivalent estimate is less certain.

By substituting the Reliability Score averages for each of the manufacturers and lines into Toyota's regression equation, we obtained the above table of Toyota age-equivalent estimates, rounded to the nearest whole year.

With regard to the computation of Reliability Score averages, I borrow the old summary:

The definition of Reliability Score begins with two observations. First, the symbols in the right-most column of a Consumer Reports auto model reliability table depicts reliability performance of categories (called “trouble spots,” by Consumer Reports) of components of motor vehicles in the approximate age range of 0 to 1 year – the exact age range depending upon when the corresponding model year began and ended and when Consumer Reports stopped accepting returned questionnaires for its compilations. Second, similarly, the second column from the right, the third column, the fourth column, the fifth column, the sixth column, the seventh column, and the eighth column depict reliability performance of the same categories of components in the approximate age ranges of 1 to 2 years, 2 to 3 years, 3 to 4 years, 4 to 5 years, 5 to 6 years, 6 to 7 years, and 7 to 8 years, respectively.

Next, some particular Reliability Scores are defined, from which may be seen a general definition. The Reliability Score RS(The Lexus LS400,1991,7-8) was obtained as follows:

1.   The leftmost column of the Lexus LS400 reliability table in the April 1999 issue of Consumer Reports was selected, as it is this column that rates problem frequencies by “trouble spots” in the 1991 Lexus LS400s that were in the age range of 7-8 years, approximately.

2.  The trouble spots of “Manual Transmission,” “Clutch,” “Brakes” and “Exhaust” were eliminated from this left-most column for reasons discussed in step 1 of the foregoing definitions of Reliability Index Value and Average.

3.   If all of the remaining 12 trouble spots had a Consumer Reports rating, the following was done. First, -1 was ascribed to each of those trouble spots that earned the lowest rating (had the highest frequency of reported auto problems. Second, - ½ was ascribed to each of those trouble spots that earned the second lowest rating (had the second highest frequency of reported auto problems. Third, 0 was ascribed to each of those trouble spots that earned the middle rating (had the third highest frequency of reported auto problems. Fourth, + ½ was ascribed to each of those trouble spots that earned the second highest rating (had the second lowest frequency of reported car problems. Fifth, +1 was ascribed to each of those trouble spots that earned the highest rating (had the lowest frequency of reported auto problems.

Next, the numbers that were obtained in 3 were added together and divided by 12. This value is the Lexus LS400’s Reliability Score:

RS(The Lexus LS400,1991,7-8).

Rather at once, it is seen that this value falls in the closed interval [-1,+1], as is the case for all Reliability Index Values.

While the above computations are for model year 1999, they likely apply to more recent model years as well, since changes in quality occur at a rather glacial pace. See Charts of Annual Shares of Consumer Reports' Used Cars to Avoid.

As the above computations are quite involved, they are not likely to be duplicated soon, and updating for more recent years is additionally complicated by the possibility that Consumer Reports may have changed the definitions of the symbols it uses, which would require an additional examination to determine whether the change, if any, is significant with respect to maintaining uniform Reliability Scores.

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