Why have Test batsmen scored less this year?

This year has been one of the weirdest for batting in international cricket. Test batsmen aren't making many runs (the average runs per wicket is 27.25); ODI batsmen are averaging more (30.11), which is almost unheard of; and T20I hitters are averaging only about three runs fewer (23.61).

Let's start by looking at Test cricket. You can break Test cricket down to a few different periods: before World War I, cricket was basic. In 1871, WG Grace made more hundreds than all other county batsmen combined. Overarm bowling was still new, so while it was raw, it was also that people hadn't played much of it. This, combined with the fact that liquid manure wasn't yet used on pitches meant the surfaces weren't flat. In the early days of Tests, batting was poor; Grace averaged only 32 in Tests and 39 in first-class cricket.

But it was Grace, one of the earliest batsmen to play with assurance off both front and back foot, depending on where the ball had pitched, who changed batting. And then Ranjitsinhji, who, through a technical flaw, ended up inventing the leg glance and opening up the field. From there we had Vic Trumper, the first batsman to hit the ball where he wanted, not based on where it was pitched.

Before the First World War, the average runs per wicket was 27.6, which was by far the highest since the start of Test cricket. After the war, it was 33.4. That's a huge jump.

That means that by the 1920s, batsmen had worked out the most efficient ways to bat on pitches that were finally flat, and batting exploded in what was the greatest era in cricket history. Jack Hobbs, Herbert Sutcliffe, George Headley, Wally Hammond, Bruce Mitchell and Don Bradman dominated. The first great wicketkeeping batsman, Les Ames, also appeared in this era. Bowling was still in transition, spinners and cutters had dominated the batsmen for years, but as the pitches changed, they had been left behind. Fast bowlers who could terrorise batsmen were still rare, and when Learie Constantine or the England team used the short ball as a weapon, it was not always handled well by cricket as a whole (see Bodyline).

The 1950s was an era on its own, standing out for its incredibly turgid cricket and poor batting. Perhaps the bowlers caught up, or maybe the fact that in the '50s batsmen refused to hit the ball off the square meant they were easier to dismiss. And India, Pakistan and New Zealand were all still struggling to improve their games.

Then cricket found a superb balance. Decade after decade there was practically no real change as bat and ball did well, with the average runs per wicket just hovering around 32. It was perhaps no real surprise that this is when Test cricket truly became great. We had, for the first time, great teams from outside Australia and England. West Indies dominated, Pakistan were outstanding, India produced greats, and even New Zealand had a magical few years. The golden age of cricket is taken to be the early 1900s, but the greatest time for the game was from the late-1970s to late-1990s.

That couldn't last, and it was the batsmen who broke the peace. In the 2000s came the second great batting era. Bigger bats, bigger batsmen, new attacking shots, and the fact that batsmen seemed to back themselves again. It is also important to remember that the '70s, '80s and '90s had the greatest collection of bowlers that ever lived. In the 2000s, there was a dip, and since then, batsmen have just smashed bowlers where they please. Until this year.

This year has the lowest batting average per wicket since 1959 and the lowest bowling strike rate since 1922 , which was the only other year after the First World War where wickets fell at less than 60 balls each. The year has not finished yet, and the collective strike rate might yet get a bump. Perhaps it's an anomaly, like the year 2000 (when the average runs per wicket was a low 29.44, before it rose again), or it could be the sign of a slip. Those who have noticed it pointed to Ireland and Afghanistan playing Tests for the first time - which ignores that those teams had to bowl in those Tests too. Or the creeping T20 mindset getting a grip on our precious, sensible batsmen.

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Since the mid-'90s we've been told that ODI batting was ruining Test batting, and yet we've just had the best Test batting period in this era of T20s. In 2014, when T20 was well established, Test players averaged an astounding 36, which is the eighth highest for all years where ten or more Test were played. Last year it was a healthy 32.1. It's unlikely that all Test batsmen have forgotten how to bat in the space of a year.

More interestingly, since 1979 (when ODIs became prevalent), there have only ever been two years when the average for an ODI wicket was more than that for a Test wicket - 1998 and 2000. In the last two years, ODI wickets have been worth 32.96 and 29.97 respectively; Test wickets have been lower both times. Now that could be a sign that teams are too cautious in ODI cricket. For all the talk about 300 being par, the only team that has averaged more than a run a ball in ODI cricket since the 2015 World Cup is England.

That ODI cricket is now more productive per wicket is not even the weirdest thing about runs-per-wicket figures of this year. T20I has almost caught Test cricket in 2018.

And the T20I averages have been rising for the last four years. By this point in the evolution of T20, with the runs per over rising every year, you'd expect the runs per wicket to be dropping. Instead, since 2014, the runs per over has risen side by side with the runs per wicket, and in 2017 and 2018 we've had our first two years where the RPO has gone past eight (excluding 2005, the inaugural T20I year, when only four matches were played in the format).

So, T20I and ODI teams are scoring quicker than ever before, and also doing so while conceding fewer wickets. And as you might expect, Test teams are also scoring quicker.

So that means the Test scoring rate is faster than any other time in history, and we are witnessing one of Test cricket's greatest ever batting eras. Until the 1960s, batting averages and bowling strike rates followed a similar path. From the '60s on, the balls faced per dismissal has fallen, even as batsmen have mostly made more runs.

Players have learned to score quicker without it affecting their averages. This means more Tests have results, and people see it as poor batting even if players are making as many runs - if not more - than in several previous eras. But according to CricViz, this year batsmen have been dismissed far more often when playing defensive shots than since we started recording these numbers in 2006. And players also play fewer defensive shots than ever before. So are they worse at it because they don't play them enough, or do they play them worse because their techniques are now set up for other formats of the game?

This year ODI batsmen have out-averaged Test players for only the fifth time ever, and T20I batsmen are within touching distance of Test batsmen. The question is whether this is a trend or an anomaly. You would think as T20I players keep testing the theoretical limit of how quickly they can score, their averages will drop again. But for ODI cricketers, it makes sense for averages to remain high as totals grow towards 400.

For Test cricketers, well, who knows?

It could just be that bowlers are working their way back into the game, a natural evolution in cricket. Perhaps after years of the CEO pitches we're now seeing slightly better playing surfaces. There are incredible bowlers everywhere. India, Australia, England, South Africa, New Zealand and Pakistan all have great bowling depth. When talking about failing batsmen, we rarely mention outstanding bowlers.

But this year - as you'd expect - with all those wickets, the runs per over has only been 3.16, well down from the mid-2000s. In fact, between 2005 and 2010, it was 3.33. Since then it has been 3.20.

As T20 has taken over the game, Test cricket has slowed a touch. You can certainly see the impact of T20 in Tests: spinners now have in-and-out fields, batsmen start with long-on and long-off out to allow them singles. But they hole out to these fielders instead of chipping the ball around.

So maybe this is the tipping point that all the old fellas have been moaning about for years - the time when Test batting is finally ruined by white-ball cricket. More likely, though, it's just a blip, or another moment in the constant evolution of batting. One thing is true: Test batsmen aren't making many runs this year. Maybe they will next year.