MARKETS-STOCKS/– Neil Unmack and Agnes T. Crane are Reuters columnists. The views expressed are their own —

By Neil Unmack and Agnes T. Crane
When some of the most influential financial thinkers of our time failed to call one of the biggest bubbles since the Great Depression before it burst, a little skepticism about the recent run-up in stocks is a healthy antidote to the cheerleading that typically accompanies big gains.

Given the enormous size of the last bubble, the current round of inflation in financial markets perhaps should be called by another name — maybe “bubblette” would better suit the times.

The hallmarks, though, are similar: Access to cheap credit helps re-inflate depressed prices, but eventually the explanations for extended gains start looking flimsy. Stocks started entering that territory in August when many pointed to better-than-expected earnings to justify the surge in prices that have taken major gauges to their best levels for the year.

The price-to-earnings ratio for the S&P 500 currently stands around 26.5 based on operating earnings for 12 months through June. That’s well above the historical average of 19.26, according to S&P senior index analyst Howard Silverblatt.