Can you remember what that was?
If you're dealing with statistics averaged from a whole bunch of data, you should check a couple of examples in more detail and see if they match the conclusions you're drawing from the whole data set.
So in this example, checking with a couple of companies to see if their wages really did stagnate.
ETA: The table linked by Landsburg has been called into serious question by Evan Soltas [H.T. CronoDAS]. I edited the post to leave only the table to provide context for the comment discussion of its status.
Economist Steve Landsburg has a post [H.T. David Henderson] about the supposed stagnation of median wages in the United States in recent decades. In the linked table median wages have risen for: