Logarithmic Loss function in Criteolab comptetion - kaggle

The logarithm of the likelihood function for a Bernoulli random distribution.

In plain English, this error metric is typically used where you have to predict that something is true or false with a probability (likelihood) ranging from definitely true (1) to equally true (0.5) to definitely false(0).

The use of log on the error provides extreme punishments for being both confident and wrong. In the worst possible case, a single prediction that something is definitely true (1) when it is actually false will add infinite to your error score and make every other entry pointless. In Kaggle competitions, predictions are bounded away from the extremes by a small value in order to prevent this.

LogLoss=−1n∑i=1n[yilog(ŷ i)+(1−yi)log(1−ŷ i)]