The reliabilities of all model years of the Ford Explorer and the Toyota Highlander can be measured using the PPMY index which is defined as problems reported per thousand vehicles per Year:
PPMY = P / S / Y * 1000,
where P = total problems reported during the life of a particular model year; S = total units sold of the model year; Y = years since the model year has been on the market (the age of the vehicle). The index can also be written as:
PPMY = [Problems / (Sales/1000)] / Age.
A bigger PPMY index indicates less reliability of the given model year cars. For example, the most problematic model year of the Ford Explorer is the 2016 Ford Explorer. This model had a total of 279,387 cars sold in the United States and had 756 problems reported as of today. The PPMY index can be calculated as:
PPMY = [Problems / (Sales/1000)] / Age = [756 / (279,387/1000)] / 2 = 1.35.
Similarly, the most problematic model year of the Toyota Highlander is the 2010 Toyota Highlander. It had a total of 84,216 cars sold in the United States and had 193 problems reported as of today. The PPMY index of this model can be calculated as:
PPMY = [Problems / (Sales/1000)] / Age = [193 / (84,216/1000)] / 8 = 0.29.
The complete results for the recent model years of Ford Explorer and Toyota Highlander are shown in Table 1 and Table 2, respectively.
| Explorer Model Year | Problems Reported | Sales [1] | Age | PPMY Index |
|---|---|---|---|---|
| 2017 | 252 | 357,721 | 1 | 0.70 |
| 2016 | 756 | 279,387 | 2 | 1.35 |
| 2015 | 638 | 224,409 | 3 | 0.95 |
| 2014 | 689 | 209,112 | 4 | 0.82 |
| 2013 | 1,004 | 239,413 | 5 | 0.84 |
| 2012 | 476 | 86,916 | 6 | 0.91 |
| 2011 | 763 | 82,807 | 7 | 1.32 |
| 2010 | 108 | 72,248 | 8 | 0.19 |
| 2009 | 34 | 25,872 | 9 | 0.15 |
| 2008 | 180 | 89,892 | 10 | 0.20 |
| 2007 | 218 | 107,108 | 11 | 0.19 |
| 2006 | 697 | 177,606 | 12 | 0.33 |
| 2005 | 531 | 197,645 | 13 | 0.21 |
| 2004 | 1,396 | 295,689 | 14 | 0.34 |
| 2003 | 1,190 | 301,251 | 15 | 0.26 |
| 2002 | 3,391 | 492,580 | 16 | 0.43 |
| Highlander Model Year | Problems Reported | Sales | Age | PPMY Index |
|---|---|---|---|---|
| 2017 | 46 | 183,951 | 1 | 0.25 |
| 2016 | 46 | 188,679 | 2 | 0.12 |
| 2015 | 103 | 193,978 | 3 | 0.18 |
| 2014 | 69 | 78,129 | 4 | 0.22 |
| 2013 | 164 | 183,941 | 5 | 0.18 |
| 2012 | 125 | 124,045 | 6 | 0.17 |
| 2011 | 137 | 84,305 | 7 | 0.23 |
| 2010 | 193 | 84,216 | 8 | 0.29 |
| 2009 | 116 | 57,162 | 9 | 0.23 |
| 2008 | 346 | 137,668 | 10 | 0.25 |
| 2007 | 108 | 78,668 | 11 | 0.12 |
| 2006 | 240 | 100,757 | 12 | 0.20 |
| 2005 | 267 | 130,149 | 13 | 0.16 |
| 2004 | 325 | 123,726 | 14 | 0.19 |
| 2003 | 299 | 128,158 | 15 | 0.16 |
| 2002 | 332 | 110,530 | 16 | 0.19 |
To study the aggregated reliabilities of the Ford Explorer and Toyota Highlander vehicles, we use the PPM index which is defined as:
PPM = Total Problems / (Total Sales/1000),
Where the total problems in the equation is the total number of problems reported for all model years listed in Table 1 (Ford Explorer, 2002 to 2017) and Table 2 (Toyota Highlander, 2002 to 2017); The total sales in the equation is the the total number of vehicles sold in the United States for all model years in Table 1 and Table 2. The results are shown in Table 3.
| Car Model | Ford Explorer | Toyota Highlander |
|---|---|---|
| Model years | 2002 to 2017 | 2002 to 2017 |
| Total Problems Reported | 12,323 | 2,916 |
| Total Sales | 3,239,656 | 1,988,062 |
| PPM | 3.80 |
1.47 |
| Note: A smaller PPM value suggests better reliability. | ||