The Decision Review System in numbers

The Decision Review System has evoked plenty of controversy in the World Cup so far, but even its strongest critic will agree that the system has helped reduce errors. A good example was the match between Canada and Pakistan, when the reviews prevented as many as five errors. The effectiveness of the DRS was on display much earlier, in the fourth match of the tournament, when three decisions were reviewed in Australia's match against Zimbabwe, and on each occasion the on-field umpire's call was reversed. (Check the match notes below each scorecard for the details.)

Along the way there have been problems, with the ICC making it more difficult for themselves and the umpires by changing guidelines midway into the tournament. A lot of good has still come out of the system, though, and a fair number of decisions have been overruled already: an average of more than one decision per game has been overturned after the third umpire has taken a close look at the replays. In 23 matches in the World Cup so far, the DRS has been used 96 times, of which the umpires' original decision has been reversed 27 times. (With better technology, that number would have been even higher.) Even in its current form, the system has helped: apart from reducing the errors, it has also helped reduce the rancour on the field as it does away with the sense of perceived injustice. For the purposes of this article, though, let's just look at the numbers in terms of the decision-making.

The success rate of 28.13% means a little more than one out of every four decisions reviewed goes in favour of the team which asks for the review. That isn't a very high number, considering the fact that you'd expect a team to exercise that option only when they're fairly sure they've been wronged, but often teams have gone for that option out of sheer desperation, or when they have nothing to lose.

This also means the on-field umpire has got it right 71.87% of the time, which is a reasonable percentage considering these are usually marginal decisions. Due to the imperfect technology, more than one incorrect decision hasn't been corrected despite the replays, but overall these numbers offer an idea of how the system has been used so far.

The table below shows that the reviews asked for by batsmen have yielded greater success than those summoned by the fielding team, which is as you'd expect since batsmen usually know when they've been wrongly given out. One out of every three reviews asked by a batsman has been overturned, while that ratio is about one in four for the fielding side.

Some of the resentment with the DRS in the World Cup has also been because all the means available to make a correct decision are not being used. It's been particularly difficult to overturn not-out decisions for caught-behind appeals due to the absence of Hot Spot - Mahela Jayawardene arguably benefited from this loophole twice in an innings against Canada. The only caught-behind review when a not-out decision has been overturned in this World Cup was when Graeme Smith was given out against England. The other successful caught-behind review was when JP Duminy appealed after being given out against England, and won a reprieve. Not surprisingly, only eight times have teams appealed against a caught-behind verdict.

And now for the performances of the teams with respect to the DRS. All teams have a success rate of less than 50%, but the best among the lost are the South Africans, who've got three out seven correct. Canada wouldn't have had too much experience of this system before the World Cup, but they've got used to the system pretty quickly, getting five correct out of 12. India haven't used the DRS much either, but their numbers aren't as good - only one correct out of six, though they'll feel aggrieved they didn't get the Ian Bell lbw decision in that tied game. The two teams with a 100% unsuccessful record so far are New Zealand and Ireland

The match in which the review was used most often was the one between Pakistan and Canada, when Pakistan called for it seven times and Canada tried it thrice, for a match total of ten. The next highest is eight, in that cliffhanger between England and South Africa. Most often, though, reviews have been used four to five times in a match, with nine games out of 23 falling in this category.

There's been no game in this World Cup so far when the review hasn't been used. Only in two matches - Bangladesh's games against India and West Indies - has the review been called upon just once.

The DRS is also a way to judge umpires, though two factors make this a task fraught with danger: so far the sample sizes for decisions reviewed per umpire are small - an argument which applies to team stats as well - and the lack of some technology means a few incorrect decisions don't get corrected by the review and end up skewing the numbers.

Among the umpires who've had their decisions reviewed at least four times, two have a 100% record in terms of never having their decisions overturned. Aleem Dar and Billy Bowden are on top, while Simon Taufel and Shavir Tarapore aren't far behind.

Most of the umpires have pretty good success rates, but for four of them, the percentage of correct decisions on reviews is less than 60%. Amiesh Saheba has had his original decision overturned four times out of nine, for Tony Hill it's three out of six, while Daryl Harper and Asoka de Silva are the only ones with a sub-50% success. Harper's decisions were overturned four out of six times in that game between Pakistan and Canada, while de Silva has had every one of his four decisions reversed when it has gone up for review.

DRS stats for umpires in the World Cup so far*

Umpire	Matches	Reviews	Decision upheld	Decision reversed	% upheld
Aleem Dar	3	5	5	0	100.00
Billy Bowden	3	4	4	0	100.00
Simon Taufel	3	6	5	1	83.33
Shavir Tarapore	2	6	5	1	83.33
Richard Kettleborough	2	5	4	1	80.00
Billy Doctrove	2	5	4	1	80.00
Asad Rauf	4	9	7	2	77.78
Rod Tucker	3	9	7	2	77.78
Kumar Dharmasena	3	4	3	1	75.00
Nigel Llong	2	7	5	2	71.43
Amiesh Saheba	3	9	5	4	55.55
Tony Hill	3	6	3	3	50.00
Daryl Harper	2	9	4	5	44.44
Asoka de Dilva	2	4	0	4	0.00

* Includes umpires who've had their decisions reviewed at least 4 times in this World Cup.