Yahoo! Germany reported an actual market value of $10.52 billion euros and an earnings yield of 36.9%

(P/E of 27). The easy part is supplementing the table:

Manufacturer Market Cap Earnings P/E Ratio E/P Yield Volvo (ADR) $5.7 −$0.18 −31.7 −3.2%

Ford $14.1 −$5.30 −2.7 −37.6%

GM $18.8 $1.83 10.3 9.7%

Nissan (ADR) $27.0 $2.55 10.6 9.4%

DaimlerChrysler $32.3 $4.63 7.0 14.3%

Honda (ADR) $37.7 $3.09 12.2 8.2%
Toyota (ADR) $87.3 $4.51 19.4 5.2%
Sum $222.9 $11.13 25.1 6.0%
Average $31.8 $1.59 3.6 0.9%
The hard part is deciding on a suitable P/E comparable. Our first method (average E/P yield, then invert)
suggests adopting the astronomical ratio of 1/0.9% ≈ 111, due to Ford’s enormous loss in terms of market capitalization (Ford had $85 billion in sales and a positive EBITDA of $4.8 billion. But Ford also has ongoing depreciation on the order of $15 billion per year, but capital and other expenditures on the order of $18 [2001] to $37 billion [2000 and 1999].) Our second method (sum up Es and Ps first) suggests $222.9/$11.13 ≈ 20, but it weighs the larger (and Japanese) firms more highly. Nevertheless, in this case, the second method came closer to the actual Volkswagen P/E multiple of 27.
Incidentally, by mid-2003, VW had introduced a couple of flops and its earnings had sagged to $2.5 billion, though its market capitalization had increased to $15 billion. This meant that Volkswagen’s P/Emultiple had shrunk from 27 to 6 in just 9months! As to assumptions, they all fall into the category of “apples like apples.”
For example, you are assuming (hoping) that leverage ratios are similar, foreign earnings are comparable, timing is the same, and so on.