Eden Hazard had a remarkable 2012-13 season in the English Premier League. Having begun the season at the age of twenty-one, he scored nine goals, of which only two came from the penalty spot, and assisted on a further eleven—all in fewer than twenty-eight hundred minutes of action. Only his then-teammate Juan Mata had more assists, with twelve; Mata also played the equivalent of one more entire match. But did this mean that the two Chelsea men were the best passers in England?

Probably not. For many years, soccer has been using assists as a measure of passing prowess on the pitch. That’s too bad, because it’s a pretty meaningless statistic.

Let’s start with the obvious. Goals win soccer games, and shots lead to goals. To take shots, teams usually need to pass the ball into a position where reaching the goal is both feasible and likely. Assists only reward players whose passes happen to result in goals. The question is whether the player whose passes result in goals more often is really a more skillful player than one whose passes are squandered.

A quick way to analyze this issue is by gauging the rate at which passes become assists. For my analysis, I used a database compiled by Opta, a sports-data firm that tracks game video, which charted all the matches in the English Premier League’s 2012-13 season. To simplify matters, I decided to look at passes and shots in open play—excluding free kicks and corners. More than six thousand of these passes led to shots, but fewer than six hundred resulted in goals.

To assess the quality of these passes, I wanted to examine players who made a lot of them. Twenty-eight players accounted for at least forty passes each, and together they assisted on a hundred and thirty-three goals. I split their passes into two groups of at least twenty—a common cutoff for statistical analyses. For each group, I calculated the ratio of assists to total passes.

Among the twenty-eight players, the ratios were virtually uncorrelated between the two groups; the correlation was in fact slightly negative (-0.13). In other words, the players showed no consistent ability to make assists. They made plenty of passes that were good enough to turn into shots, but the smattering of goals that resulted was essentially random. This may have had as much or more to do with inconsistency among the shooters as it did with the passers.

But not all passes are created equal. The ones that put shooters in a better position to score ought to be worth more when evaluating a player’s skill. For example, a Hazard pass that places the ball right at a striker’s feet, just ten yards from the goal, is more valuable than a long cross that finds a striker among several defenders on the edge of the eighteen-yard box, giving him no choice but to take a poor shot. Yet judged by this standard, much of what may seem like ability may have to do with where players usually operate on the field. An attacking midfielder like Hazard, who skirts the edges of the penalty box, doesn’t have to pass the ball as far—or as often—to generate a good shot as a defensive midfielder who hangs around the halfway line.

So how can we figure out whether some players’ passes give shooters that little extra advantage when it comes to scoring goals? One way is to use a concept called “expected goals.” Essentially, every shot has some ex ante_ _probability of becoming a goal, depending on the situation leading up to it, where it was taken, and whether the foot or head was used. When these probabilities are estimated using historical data and summed up for a player or team, they show the expected number of goals that the player or team would score given their shots. In most situations, shots taken far away from the goal or at acute angles have a lower chance of scoring, as do headers.

Some passers yield shots with higher expected goals than others, but again, this has a lot to do with where they play. This graph compares the locations where passes originated with the likelihood of the passes becoming assists:

Asking how many assists a player has, or even how many assists he’s likely to have in the future, has a lot to do with how far downfield he usually plays. The answer won’t necessarily have anything to do with his talent; in fact, it might depend more on the quality of the shooters playing alongside him. If we truly wanted to gauge whether a player showed exceptional passing skill, we might ask whether his passes led to better shots than other players’ passes, even for the same shooter.

To answer this more subtle question, I computed a value for each pass that led to a shot. I started with the expected goals from each resulting shot and subtracted the average expected goals per shot for the same shooter. But for the second part, I only averaged the shots he took after receiving the ball from other passers. Then I took these pass values and averaged them for each passer to see if he was routinely serving up better balls.

I’ll call this average a passer’s “delta.” Looking just at players with forty or more passes, the ones with the highest delta in 2012-2013 were Gareth Bale, then of Tottenham Hotspur, at 4.4 per cent; Robin van Persie, of Manchester United, at 3.7 per cent; and Samir Nasri, of Manchester City, at 3.1 per cent. All of them took the field as attackers, but passers didn’t always have to play so far forward to rank high on the list; the fullbacks Glen Johnson, of Liverpool, and Leighton Baines, of Everton, were also in the top ten. Hazard was thirteenth.

Seventeen of the twenty-eight prolific passers supplied balls that led to better-than-average shots for their fellow players. To find out if they did it consistently, I again split the passes into two groups and compared the players’ deltas. This time the correlation between the groups was moderately high and positive, at 0.57, for the twenty-eight prolific passers. The delta for passing quality may indeed be a reliable indicator of ability.

Of course, delta is only a measure of pass quality, not pass quantity, which we might measure as passes leading to shots per minute played (though this, too, would depend in part on shooters’ skill). No one had both a higher delta and a higher passing rate than Mata during 2012-13 season, but second place by these criteria went to Luis Suárez, of Liverpool, not to Hazard. Judged by assists, however, Suárez, who had just five, would have been tied for twenty-fourth in the league with thirteen other players. During the next season, he had twelve assists—and I doubt very much that his passing ability had spontaneously doubled.

The distinction between passes that turn into goals and passes that turn into other shots–often called “key passes”—is largely meaningless when it comes to evaluating players. Some players appear to have a consistent ability to deliver passes of above-average quality. Assists just aren’t a good way of measuring it.