The market sell-off may still have a few more stocks to take down to size, according to historical valuations. A rough year for Wall Street got even worse on Monday, as stocks opened sharply lower and the S & P 500 set a new intraday low for the year. The selling was widespread, with every member of the benchmark index falling in morning trading , but some stocks look more expensive than others. Despite the broad declines, many stocks are still trading well above their historical averages, as measured by their price-to-earnings ratios. The stocks below, for example, are trading above their 5-year average P/E ratio despite falling more than 15% this year. Source: FactSet The biggest outlier on the list is American Airlines . Travel stocks including airlines have had dramatic shifts in projected earnings in the Covid era, which can make average P/E a noisy number. Still, American traded at around 9-times-earnings in mid-2017, long before the pandemic, and far below the nearly 33 it was trading at as of Friday’s close. The stock trading at the second-highest valuation relative to its own history is Fortinet . The cybersecurity stock is trading at a whopping P/E of nearly 52. Data security is seen as a future growth area, but investors have increasingly turned their backs on companies whose big payoffs are years away. The biggest name on the list is Apple , though it was only trading slightly above its average valuation. The iPhone and iPad maker has a massive cash pile that has many investors to see it as a relatively safe stock in a growth-focused sector, but its shares are still down more than 20% year to date. Retailer Costco is also trading at a slightly higher than normal valuation, despite concerns about consumer spending and inflation. Costco’s subscription model can make it more attractive to investors than its retail peers during uncertain times, but a recession could drag down the whole sector. Making matters worse, the price-to-earnings values shown above might still be too optimistic. As signs of an economic slowdown have mounted in recent weeks, some Wall Street strategists have predicted that analysts will soon be forced to cut their earnings forecasts. That would make these stocks even more expensive on a historical basis.