Slope Graphs and Heat Maps
A previous Infogol blog explained how expected goals (xG) – the process of chance creation, together with a quantified estimation of each individual chance created and faced by a side – is a better indicator of performance than the often luck driven singular outcome of those chances.
Using the xG data for each team, we are able to derive the percentage chance of each match outcome (as opposed to the actual result) for both games played and matches yet to take place, which are used to generate both Expected and Forecast League positions.
The Expected League position is the number of points that a team might have been expected to accrue based on their performance thus far, as judged by the Infogol model, which has simulated the match thousands of times over to arrive at those percentage chances for each outcome.
The Forecast League position uses the points that a team have already accumulated in the current season, while also taking into account their underlying xG stats and historical performance, to predict where they will finish at the end of the season.
The Infogol App showcases Expected and Forecast positions in the League tables in the Stats category.
Another way to express this information is in the form of a Slope Graph.
The Slope Graph gives an at-a-glance guide to a team’s expected (based on performance thus far), current (actual) and forecast (their current position and simulated results of remaining games) positions, so as you can easily identify whether they are under/over performing compared to their xG. Generally speaking, a downward slope indicates a team that is under performing while an upwards one suggests a team is over performing.
Taking the Slope Graph for the Premier League as showcased here, before match day 25, you can see that xG data suggests Crystal Palace, Southampton and Leicester could have been expected to have more points than they actually had, while at the other end of the scale Burnley and Watford have arguably overachieved in terms of their points haul.
A Slope Graph, however, is the most probable outcome from a range of possible ones. So, for example, a team may be forecast to finish 7th, which is where they will show on the Slope Graph, but there is uncertainty around this forecast position and their range of final positions may actually be from a high of 4th to a low of 14th.
This uncertainty is shown in the Infogol Heat Map.
The Heat Map shows the probabilities for each team to finish in each position in the table via the colour scale – the deeper the red, the higher the probability. It orders the teams using their highest probable position, which corresponds with the Forecast League position in the Slope Graph.
The Heat Map for match day 24 shows, as you might expect, that Chelsea (who have over performed only slightly) are strong favourites to win the league and that Everton’s most likely finishing position is seventh, but that there are a wide range of possibilities for some of the other teams, such as Manchester Utd whom it is predicted could finish as high as second.
As the season progresses, both Expected and Forecast League positions will change, so make sure you check the Infogol app for the latest updates.