Is the Firm Cyclical?

Firms that go through boom and bust cycles - semiconductor companies and auto manufacturers are good examples - require a bit more care. Although you'd typically think of a firm with a very low trailing P/E as cheap, this is precisely the wrong time to buy a cyclical firm because it means earnings have been very high in the recent past, which in turn means they're likely to fall off soon. For cyclical stocks, your best bet is to look at the most recent cyclical peak, make a judgment whether the next peak is likely to be lower or higher than the last one, and calculate a P/E based on the current price relative to what you think earnings per share will be at the next peak.