Certain conversations form the soundtrack to an Australian cricketing summer.

Be that Jim Maxwell giving the latest score before teeing up the news headlines on the hour; a travelling commentator waxing lyrical about a part of the country they just visited (usually involving a winery); and, perhaps most consistently of all, talk turning to how the Australian selectors should just pick the batsmen with the best Sheffield Shield averages instead of relying on gut instinct or that nebulous concept of 'potential'.

It is a simple, compelling argument.

But, with apologies to Matthew Wade and his supporters, one where the numbers in part at least — with a heavy serving of irony — just don't stack up. Sheffield Shield averages do not provide the clear correlation with Test performance as might be imagined.

Matthew Wade's Test case has been ignored by selectors despite a Sheffield Shield average of 63.44 this season. ( AAP: Rob Blakers )

The ABC has examined the career Shield and Test averages for all 456 Australian Test players, excluding those who didn't play Sheffield Shield cricket (the competition only started in 1892, while Australia started playing Tests in 1877). At first look, there seems to be a relationship between a player's Sheffield Shield average, and their Test one.

However, you'll note the large number of entries concentrated around the bottom left of the above chart — made up almost exclusively of bowlers.

It is this sample that provides a Shield average its predictive weight. When you remove players with a Shield average of less than 30 (i.e. non-specialist batsmen), the relationship significantly deteriorates.

The below chart shows that once you remove the bowlers, the weight of a player's Shield average evaporates.

For some, a successful technique at first class level can fall apart in the Test environment. For others, the value of a player's wicket (and their tenacity) translates as well (or better) when there is more pressure in the matches.

For the upcoming series against Sri Lanka, Australia has overlooked several prolific run scorers, including Shaun Marsh (currently leading the Shield averages, minimum six innings), Matthew Wade (3rd) and Nick Larkin (5th), for players such as Marcus Harris (2nd), Kurtis Patterson (6th), Joe Burns (7th), Marnus Labuschagne (30th) and Matt Renshaw (46th).

The value of three figures

Just after the squad selection for the Tests against Pakistan in the UAE last year, the media arm of Cricket Australia revealed the statistical factors behind the team picked, and a strong focus was put on the ability to score centuries at all levels (even if the leadership of the side didn't know initially how to count up centuries across different formats accurately).

The likelihood that a player can make a century at Shield level is almost as good a predictor of his Test career as that of his raw average. That is to say that neither measure is particularly robust in predicting performance at that higher level.

Two players stand out as a good example of the unpredictability of this data — Michael Bevan and Ricky Ponting. Both players managed to convert a given innings into a ton about a quarter of the time when they went out to bat, but while Ponting managed 41 Test centuries from 287 innings (a 14.3 per cent conversion rate), Bevan managed none from his 30 innings.

Further, and unsurprising to most, knowing a player's likelihood to score tons in one day matches (both at domestic and international level) offers little value in assessing his ability to either score centuries or score big in the Test arena.

In fact, there is actually a negative correlation in the ability to score centuries in domestic one day cricket to scoring them in the Test arena. There is also a negative correlation between the likelihood of scoring centuries in domestic short form cricket and Test averages.

In layman's term, it's not just a non-factor, it might be a negative attribute for a player.

The reason for this will vary between players. But one potential impact is that aggression, often early, is usually required to score centuries in limited overs cricket, whereas at Test level patience is more often required, and mistakes are pounced upon by top level oppositions if a player employs an approach in the long form of the game that is similar to their limited overs approach.

Some players have both in their locker. But one does not guarantee the other.

Something to consider for those like Shane Warne offering up D'Arcy Short as a solution to the current top order problems. Or selecting Aaron Finch to open for that matter.

The added weight of recent form

Taking the long term view, the entirety of cricket history effectively, is great in terms of getting a big sample of players, and comparing across eras of success and failure. But most fans will be interested to see if this assessment holds up in the last decade or two.

The answer is: barely.

With multiple changes to the Shield and JLT Cup rules and formats over the past decade or two, it appears the once-strong breeding ground of domestic cricket has become more of a crapshoot, at least from a statistical perspective.

Although there are much smaller sample sizes involved, it appears that much of the value behind the long-held wisdom has disappeared. Some of this has to be put down to the aforementioned fiddling with the formats — without long-term rule certainty, it may be hard for players to find a rhythm in certain competitions, especially when they deviate further from the rules of Test cricket.

Shield averages in the year before a player is first tabbed for the Test team also appear to have a limited (if any) relationship with a player's long-term Test average, with form often running cold after being hot.

In short, this old rule of thumb — that weight of runs in domestic competitions should be the primary criteria for selecting Test batsmen — may no longer be the right way forward.

It's much more likely that more advanced analysis, such as looking at play and miss rates, launch angles, shot scoring areas and shot success rates will play a bigger (and more fruitful) role in selections going forward — in conjunction with the traditional statistics.

No one is suggesting Sheffield Shield performances should be disregarded, just that they should form one part of the equation only.