PLFantasy

When trying to obtain data for use in any kind of forecast you are faced with any number of questions with varying degrees of complication. Is the data from a reliable source? Do we have enough of it? How should it be interpreted? When is it stable enough to be relied upon? That latter question is where this post will focus. Generally, more data is better than less data. Nate Silver fans’ ears will prick up at that simplistic statement as his excellent book The Signal and the Noise is full of instances where too much data can cloud our judgement, but for our purposes let’s say that when trying to judge the quality of a team you’d prefer to have data for 10 games rather than 5 (data from every game in Liverpool history would start to be too ‘noisy’ as Bill Shankly or Ian Rush have little bearing on the current crop of players). After two games last season, Everton had amassed 42 shots (26 SiB) giving them a crazy 21(13) average. While the team played well the rest of the way, their...

At this point of the year it's important that we try and establish what numbers can be believed. In other words: how small is too small for a sample size? Consider, for example, that through six gameweeks last season: Aston Villa ranked 10th in goals scored at home and 3rd on the road. They wound up being the 2nd worst attacking side in the league, managing to notch just one goal more than Stoke.  Tottenham placed 19th in home defense, shipping an average of 2.5 goals per game. They finished the year as one of the league's best defenses, ranking 4th at home and 5th on the road. QPR conceded just one goal in their first three away games. They went on to concede 40 more in the next 16, at an alarming rate of 2.5 a game, enough to rank behind everyone outside of lowly Blackburn. We could go on and on. The point being, six games is not enough to write teams off or buy into short lived success. When then, is long enough? Using data from the past two seasons (ideally we'...