The form fallacy

Any time one of the league's better players struggles for goalscoring form and then breaks his drought, you will inevitably hear the commentator point out that while his poor 'form' was temporary, his class is permanent. We aren't here to perform autopsies on former stars of previous decades to suggest their class was anything but permanent, but instead we will examine the very notion of 'form' and how this is reflected in a player's goalscoring record (and hence fantasy success).

A player is described as being 'in form' under two distinct scenarios. The first is where a (rare) commentator has actually watched all of that players' games, assessed his overall performance and concluded that he is playing up to his full potential. The second, and much more common occurrence, is where an 'expert', or more pertinently here, a fantasy manager, will assess that a player is in form because he's scored a couple of goals in the last few weeks.

We are obviously interested in the second scenario, and more precisely, whether players score more goals following a game in which they found the back of the net. We will expand the analysis to assess the likelihood of a player scoring following a scoring streak of one, two and three games.

The madness in the method
We want to ascertain how often a player follows up a goal scoring performance with another goal scoring performance, and then how this compares to their standard goal scoring rate. We will look at how often players follow one, two and three game scoring streaks to try and identify the value of 'form'.

	All	FW	MD	DF
Scoring Games (SG)	837	336	374	127
Scored in next game	123	66	56	1
%	15%	20%	15%	1%
Back to back SG	123	66	56	1
Scored in next game	38	18	19	1
%	31%	27%	34%	100%
Three in a row SG	35	17	18	0
Scored in next game	11	5	6	0
%	31%	29%	33%	-

As expected, scoring last week does not have much predictive value for scoring this week (just 15%). The first lesson then is to not chase points based on a single performance alone. If a player is a recent signing or has suddenly been deployed in a new position his goalscoring may be indicative of future success, but chances are the predictive value is low.

If a player has scored in back-to-back games (or even three in a row), on first glance it appears that there is fairly strong evidence that his success will continue in the next fixture (31%). However, the proportion of goals scored by the top players is obviously disproportionately high and so you need to see the rate at which each player normally scores goals to understand the context.

The below table shows the 'streakiest' players from last year, based on the difference between the rate at which they normally score goals ('Score %') and the rate at which they scored a goal following a goal in the prior week (GW1%), having scored in back-to-back games (GW2 %) or following a scoring streak of three games (GW3%):

Not the worst list of players but aside from Meireles (who scored in 5 straight games and then never again), Adam and Kuyt the majority of the group failed to continue their 'form' across all three categories and thus we have to doubt if there's anything more to their streaks than blind luck and random chance.

Top guns
Rather than look at random players, let's turn our attention to the league's top scorers and see if any of them showed a propensity for hot streaks:

In short, there is very little correlation here. Some players had success in the games following goals, but nothing really to a degree that indicates other than a normal distribution of results. It seems that the only players who consistently showed a higher likelihood of following up a scoring performance with a goal played for Liverpool with the aforementioned Meireles, Kuyt and Adam joined by Maxi Rodriguez here. That may say as much about that team as the individual players though, and could be a separate avenue worth exploring (does a team's form or their opponents' strength dictate the result more?).

This season
Has anything changed this year? Are we seeing any different trends of predictable players? Is the world really going to end?

The top two names obviously stand out as a couple of elite players who have shown a strong tendency to follow up scoring performances with another, whether looking at a scoring streak of one, two or three games. However, Van der Vaart actually just has the one streak of five games, while Rooney has two streaks of five and three games respectively. Considering a distinct lack of 'streakiness' last year, it is therefore tough to read too much into these numbers.

The point here is not to get into individual players but to focus on the fact that, if you measure 'form' in terms of goalscoring, there is little evidence to really suggest that players consistently get 'hot'. There isn't any evidence to suggest you should shy away from players who scored last week either (indeed it is probably foolish to bench a Rooney or Aguero coming off a good game) but you should be thinking twice about bringing a player in based on a 10 point fantasy gameweek which was built on a goal from a single shot on target and the inevitable three bonus points that follow. Even two or three game scoring streaks can be fools gold if not backed up by sustainable underlying stats (shots on goal, particularly those on target).