The FTSE 100 is packed with miners and oil companies. It's partly why the index has plunged in recent weeks, led by Glencore's latest crash and burn.
China and relentless speculation about US interest rates also explains why volatility has remained above the magic 20 level for the longest stretch since the beginning of 2012.
Typically, when the market turns sour, small company shares underperform. They're the growth stocks that do well when the economy flourishes, but struggle when it doesn't. A flick through the history books tells us that default risk, interest rate risk, and inflation risk can all make things harder.
Coming out of a recession, these small companies tend to do much better. It's not completely clear where we are in the cycle right now.
GLOBAL GROWTH CONCERNS
Economies have bounced back since the financial crisis, with balance sheets repaired and prospects infinitely brighter. In recent months, however, concerns about growth have arisen, particularly in the US and China.
Global growth forecasts have been cut. The International Monetary Fund did in July and is widely tipped to do so again soon. A fortnight ago, the OECD trimmed estimates for this year to 3 per cent and to 3.6 per cent for 2016 from 3.8 per cent back in June.
'Global growth prospects have weakened slightly and become less clear in recent months,' OECD chief economist Catherine Mann told Reuters.
Barclays is slightly less optimistic, but its global economics team do not forecast recession; instead, tipping world economic growth to accelerate in the second half of 2015 to 3.2 per cent from 2.9 per cent in the first half, and then 3.4 per cent in 2016.
It thinks that with cyclical sector valuations back to lows seen during classic bull market corrections of the past, their relative performance has undershot global GDP.
DAVID VERSUS GOLIATH
A look at the performance of large-cap versus small-cap shares throws up some big surprises.
Our sister website Interactive Investor ran the numbers and found that since the market bottomed out following the financial crisis in mid-March 2009, the FTSE 100 has risen 72 per cent compared with 92 per cent for the Aim All-Share index.
Small-caps were all but wiped out in the crash, so had more to gain on the way up following a wave of cost-cutting, balance sheet repair and economic recovery.
But that's a six-and-a-half year view. Over five years the tables turn. Less nimble large-caps have caught up, and the FTSE 100 is 8.3 per cent higher.
Aim, on the other hand, is down 6.7 per cent. In fact, as the bottom chart below shows, Aim has been thrashed over five years by not only the top 100, but the Dow, Nikkei and Dax, too.
Over three years it's a 5.6 per cent gain for the blue chips and 2.8 per cent for Aim. But after that, the junior market takes the lead again - a 4 per cent decline over the past 12 months is way ahead of its top-tier rival, down 11 per cent. In 2015, Aim is up over 3 per cent and the FTSE 100 down nearly 8 per cent.
FTSE 100 versus Aim performance in 2015 to date
FTSE 100, Aim, Dow Jones Industrial, Nikkei 225 and DAX performances since 2010
Since the Footsie peaked on 27 April, it's fallen 14.3 per cent compared with Aim's far more modest 3.9 per cent decline, and since the latest sell-off mid-August, Aim is down 3.4 per cent but the large caps 8 per cent.
Alistair Strang, technical analyst at Trends and Targets, has a guess at what's going on. 'All the other markets recovered quite substantially from their lows in 2009 whereas the Aim hasn't moved anywhere near as flamboyantly as even the Footsie (which is one of the slowest and least flamboyant of the markets),' he says.
'It's resulting in a curious situation of the Aim not having as far to drop, simply because it never really climbed much anyway in the first place.'
And which companies are driving this outperformance? Here are Aim's top 10 performers since 27 April, plus how Aim's heavyweights have fared: