# Filed under Regression to the mean …

## Season to season regression of team shooting percentage in the MLS

Benjamin Massey has basically done all of the leg work for me to write this. In this post Massey put together five seasons worth of team shooting percentages and looked at how they regressed cumulatively over time. With permission I’m going to take those numbers, and essentially repeat the methodology of this post from April … Continue reading

## Sh%, Sv% & PDO, part n

This is a post designed to illustrate what I’ve previously written about shooting percentage (parts I and II), save percentage (parts I and II) and PDO (parts I and II). The aim is to show graphically how regression to the mean occurs. The method I’ve used is as follows. First I’ve determined each teams sh% … Continue reading

## Hull City 08-09 & West Ham United 06-07: Two very different ways of staying up

Both Hull City (in 08-09) and West Ham (in 06-07) survived on the final day of the premiership season. Loooking back at those teams they were both effectively saved thanks to a run of 9 games. For Hull it was their first 9, where they picked up 20 points and looked like they could be … Continue reading

## Regression to the mean can be a bitch! (Ask the nearest Blackpool fan)

I’ve wanted to do a post about Blackpool for a while and I think they give me a perfect example to demonstrate a few things I’ve been talking about recently. In particular they are the perfect model of regression to the mean in action. After a flying start to the season they’ve sunk rapidly down … Continue reading

## PDO – part II

My two previous posts have looked at how much team shooting percentage and team save percentage regress to the mean in consecutive seasons. Now I’m going to do the same for PDO. As a quick reminder PDO is calculated as follows: PDO = 10 X (Shooting percentage + Save percentage) As the premiership average sh% … Continue reading

## Save percentage – part II

Last time I took a look at team shooting percentage and came to the conclusion that it isn’t a repeatable skill, regressing >60% towards the mean over consecutive seasons. This time I’m going to look at team save percentage in the same manner. When I initially looked at save percentage I found that all teams … Continue reading

## Shooting percentage – part II

When I last looked at shooting percentage I found two things. The first was that there isn’t a large difference in sh% between a good and bad team; a top 4 team will have an average sh% of ~24%, whilst the worst teams average ~20%. The second was that there is a large variation around … Continue reading

## Predicting future performance

In my last post I plotted team points in consecutive seasons to illustrate how to calculate regression to the mean. It also serves a purpose in this post so I’ve included it again, with points scored in year 1 (eg 2000-01) plotted on the x-axis and points scored in year 2 (eg 2001-02) plotted on … Continue reading

## A primer: Calculating regression to the mean

Recently I explained the basics of regression to the mean and why I’m going to apply it to football. I want to briefly expand on it by explaining how it’s size is determined for a particular parameter. It’s pretty simple to calculate and I’ll use the example of team points in consecutive years. The first … Continue reading

## A primer: regression to the mean

Imagine you take a fair coin (one with equal chance of getting heads or tails) and flip it ten times. The average (mean) result would be to flip five heads (as the coin is fair) but you find that you actually only flip two. You then repeat the experiment and get four heads. The mean … Continue reading