Did you know that Lucas is as good a player as Mascherano? I wasn't so sure, and I'm still not, but just the other day the OP of a thread claimed this as a practically indisputable fact based on a statistical breakdown of the performance of the two players over the course of last season.
The point has been made several times during the past 12 months, and indeed it is remarkable how similar the two players look when reduced to numbers and percentages. But while such stats can be illuminating, it might be time to consider, how much and exactly what you can actually prove by breaking down performances into numbers like this.
As the thread mentioned started with the claim that the stats offered "proof", it is safe to say that there is a school, which sees statistical analysis as offering incontrovertible evidence that can be used to establish a claim as an indisputable fact. Opposed to that is the notion that football cannot be effectively analyzed statistically in a way that sheds light on any deeper truths.
The blog entry, which the OP mentioned referred to, offered a "stat off" between Mascherano and Lucas and made some basic comments to the effect that the stats were remarkably similar, but made no far-reaching conclusions, leaving the statistics to speak for themselves. The question is: Can they really do that?
Let us take some examples. The stats mentioned include:
Tackles attempted: Masch 268, Lucas 285
Tackles won: Masch 181, Lucas 180
Success Percentage: Masch 67%, Lucas 63%
A similar method is applied to passing.
Indeed, on the basis of these numbers, you would conclude that the two players were just about equally good. The stats make a compelling case, and they are hard to argue with. But in all this, it is easy to forget an important question:
Are all tackles equal?
Are all passes equal?
In other words, what do these numbers really reveal when taken out of context.
This is an important question, because it is possible to perform a thorough statistical analysis even of relevant factors without revealing much of any value.
For example, few would argue against the ability to write complete, well-constructed sentences or conjugate verbs correctly being important parts of a writer's craft, but I doubt that anyone would find an argument over the greatness of Hemingway vs. Steinbeck based on a statistical breakdown of the number of well-constructed sentences or correctly conjugated verbs very illuminating.
The things that really matter in this comparison defy statistical analysis. We should make sure, that our statistical analysis of football players doesn't become equally nonsensical.
And here the problem is that passes are not equal, and neither are tackles for that matter.
The case of the passes is probably the most illustrative one. It should be safe to say that the concept of statistical analysis of sports is one that is imported from the US, where it plays an important part in sports coverage, and where it can indeed seem very illuminating at times. But when it comes for example analyzing completion percentages, there is a fundamental difference between NFL football and the game that the rest of the world calls football. When a quarterback completes a pass, it is practically always positive. It benefits his team every time he completes a pass, and so his completion percentage is a valid measure of his performance, even if it cannot necessarily stand alone.
Not so in "real" football. Here the players with the highest pass completion percentages are often players that only rarely make any key passes. The two CBs in a back four will often have very high completion percentages, simply because they play many passes without being under any kind of pressure, and their completion percentages say next to nothing about their ability to make a key pass to send a teammate clean through on goal.
In NFL football, passes are equal. In association football they are not.
And the reason why passes are not equal is, that the difficulty and value of completing it varies greatly with the position that it is played in and with its purpose. It also varies greatly with the quality of the opposition.
Even when you compare two players in similar positions, the all season breakdown doesn't take the quality of the opposition into account. It is possible to argue that there is a randomization factor, which for all practical purposes evens out this difference, but with teams rotating and resting key players for big matches, that is by no means certain. And numbers from a game against Reading are not really comparable to numbers from a game against Real Madrid.
In other words, two players can arrive at the same number in very different ways and under different circumstances, meaning that a 90% completion rate is not necessarily comparable to a 90% completion rate. Which obviously reduces the value of this number as "proof" of a player's quality vis-a-vis another player.
The same is true for tackles.
Completely lost in the statistical breakdown is, of course, the intangibles that do not lend themselves to easy quantification. The impact of a player on his teammates is hard to measure, but can be quite decisive in real match situations. Two CBs can have very similar numbers, but in a real situation the fact that one is very slow while the other is very fast might greatly affect the willingness of their teammates to push forward, depending on who is behind them.
All this limits the reach of the conclusions that you can draw from a statistical breakdown of players. Statistics can be highly illuminating in some cases, and can often function as a valuable corrective to deeply held prejudices, but as proof they are often more ambiguous than they seem.
To return to the question of the thread mentioned in the beginning, this means that the stats do not really "prove" that Lucas is as good as Mascherano. Nor do they prove the opposite. They strongly suggest that they were about equally effective in the matches they played during that season, which is not quite the same given that the quality of the opposition could have varied. But they don't prove it, because the impact on teammates is not quantified and taken into account.
So in determining the quality of two players compared to each other, the stats don't suffice, even if they can be helpful at times. There is, in the end, not really any way around the classic Eyeball Mk. I analysis of how the players perform over a number of matches against the best opposition available.