Why captains should field first in day ODIs

S Rajesh talks about the bias towards the winner of the toss in day-night ODIs in this Numbers Game column. He says that this bias is less pronounced in day games. This masks a couple of underlying facts – there is a substantial bias towards the team batting second in day ODIs, and captains aren't as aware of it as they should be (though they may be learning). This bias is probably caused by the natural advantage the teams batting second have (in knowing precisely how many runs they need to win) and perhaps some help from early-morning moisture.

First of all, let's look at the overall results between top-eight sides since 2000. In day games, the side batting first has won 144 games and lost 204. In day-nighters, the corresponding figures are 202 and 167.

The probability that such imbalances would happen by chance are about 7% and 0.1% respectively – there's still some reasonable chance that day-nighters are fair, though I would agree with those who say that it depends on the ground. Clearly the night-time conditions are having a big effect (after all, the direction of the bias is reversed going from day to day-night), and it seems reasonable that the atmosphere in different cities would affect the white ball differently under lights.

It's interesting to break these results down further. Day-nighters, win the toss and bat: win 165, lose 123. Day-nighters, win the toss and field: win 44, lose 37. That latter result is not statistically significant, but it is at least suggestive that captains know what they're doing when they bowl first in a day-nighter.

Day games, win the toss and bat: win 55, lose 90. Day games, win the toss and field: win 114, lose 89. Clear message to captains: don't bat first in day ODIs.

Since 2000, captains batted first in about 42% of day ODIs, as opposed to 78% for day-nighters. Clearly they're aware that it's often better to bowl first in day games, but 42% is still far too high.

In 2008, though, there have been just four day ODIs where a captain has won the toss and batted, and seventeen instances of winning the toss and fielding. Are the captains learning or is it just a blip? We'll find out over the next couple of years.

I'd like to thank Pelham Barton for some discussions on this topic.