Is the main job of a bowler to take wickets or contain runs? Which is better off 4 overs, 4/40 or 0/16? They are all interesting questions.
In a large degree limited overs is much more interesting statistically than test cricket. Because there are finite resources, and more than one of them, the analysis can be quite different to what is required in the full game. The concept of batting and bowling averages are easy to calculate and are effective for telling us who is the best performers in the longer form. But someone that averages 18 and goes for 12 an over in T20 is not really as useful as someone who averages 24 and goes for 6 an over.
So I tried to see if I could quantify the value of a wicket in this years IPL. To do this I looked at every innings total. I found the run-rate (using 20 overs for any team that was bowled out) for them, and then put them into a graph, to see if anything interesting came out.
In the process I noticed something: in almost every game the team that lost the least wickets won. In the 42 games where the teams lost a different number of wickets, the team that lost the least won on 33 occasions. That's 78%. To put that in perspective, when teams score 180 they only win 69% of the time. So losing less wickets is a better predictor of winning than scoring 180. This was a surprise to me.
Next I looked at the graph:
While it is obvious that wickets lost are not the only factor that determine the scoring rate, it is also clear that there is a relationship between the wickets lost and the run-rate.
I had previously been a fan of Glenn Turner's theory of "You're all out after [20 overs] so you shouldn't leave any wickets out there" over Richie Benaud's theory of "It's a cardinal sin to get bowled out before your overs are up." However, it looks like Richie has actually got the better theory. It is clear that (generally) if a team loses more wickets, they end up scoring at a slower rate. Now clearly the timing of when the wickets fall is important, but this graph suggests that it's not as important as we would have thought.
The other interesting thing here is that this gives us a value for a wicket. Every wicket, on average, results in a team scoring 0.25 less runs per over in their innings. Hence every wicket is worth (a surprisingly low) 5 runs.
This allows us then to compare some of the bowlers, and see who has actually been the most effective in the IPL.
If we consider that every wicket is worth 5 runs, we can subtract 5 from the runs a bowler has conceded for every wicket that they have taken, and then we have a fair way to compare them, by looking at their economy rates.
Here is the table of the best bowlers in the IPL so far. (min 10 overs)
At the top, as we expect is the magnificent Lasith Malinga, who has proved his doubters that he more than a one-trick pony. But the real interest for me comes form the next 3 names. All of them are KKR players. When we combine them with Brett Lee who is further down the table, it isn't difficult to see why they have been the hardest team to score against throughout the tournament.
