From 1963 through 2015, idiosyncratic risk (IR) is high when market risk (MR) is high. We show that the positive relation between IR and MR is highly stable through time and is robust across exchanges, firm size, liquidity, and market-to-book groupings. Though stock liquidity affects the...

Since 1965, average idiosyncratic risk (IR) has never been lower than in recent years. In contrast to the high IR in the late 1990s that has drawn considerable attention in the literature, average market-model IR is 44% lower in 2013-2017 than in 1996-2000. Macroeconomic variables help explain...

Except for relatively short but intense episodes of high market risk, average idiosyncratic risk (IR) falls steadily after 2000 until almost the end of our sample period in 2017. The decrease has been such that from 2012 to 2017 average IR was lower than any time since 1965. The secular decline...