Four years ago, before the 2008 recession, Apple (AAPL) was trading at more than 45 times earnings. Today it’s trading at less than 15 — a situation that frustrates investors no end.

A little over a week ago, Dirk Schmidt, a German management consultant writing on one of our favorite blogs — Horace Dediu’s Asymco — posed an interesting question: “As Apple seems to be getting punished for growth, we have to also ask if it is the only one.”

To answer his own query, Schmidt looked at the change in Apple’s price-to-earnings ratio before and after 2008 and compared it with a dozen similar tech companies, from Google (GOOG) and Microsoft (MSFT) to Hewlett-Packard (HPQ) and Dell (DELL). He came up with the chart above and concluded, as he put it:

“There was a premium on Apple’s valuation before crisis and there is a premium after the crisis. The notion that Apple has been single-handedly punished by the market does not hold in the context of comparable companies.”

But as Schmidt himself acknowledged in the very next sentence, this comparison doesn’t take into account Apple’s astonishing earnings growth. “The next step,” he wrote on Aug. 27, “will be to determine if the P/E premium for Apple is consistent with its growth premium.”

Having waited more than a week for Schmidt to take the next step, we decided to take a stab at it on our own.

Modifying a technique Dediu used Friday to quantify what he called “the phobia of owning Apple shares,” we divided Apple’s P/E ratio by the earnings growth it reported last quarter: 121.9% year over year. Then we performed a similar calculation for a few of Apple’s closest competitors. The result is the chart below:

As you can see, when earnings growth is factored in, HP, Google and Microsoft investors are paying a stiff premium for performance that’s considerably weaker than Apple’s. Only Dell — whose P/E fell nearly half as much as Apple’s after 2008, has a comparable P/E/growth ratio.

Another way of looking at it is that Apple is, as Schmidt might put it, getting punished for growth.

According to Dediu, he and Schmidt are working on “a comprehensive analysis of how P/E and growth are correlated between comparable companies as well as over time.” They’ll do a better job than I could. We’ll add a link as soon as it gets posted.

UPDATE: Dediu and Schmidt have published a series of articles looking at the question from more angles than I would have dreamed possible. Their final take, posted Sept. 13, culminates in the vector graph copied below. See here for an explanation of what it means, and for links to the other pieces in the series.