Adding 0.5 to cells when calculating odds ratios, d' and the empirical logit transform

On the use of adding 0.5 to cells to define an odds ratio

• Subbiah and Srinivasan (2008) note the practice of adding a constant to a zero cell to define an odds ratio. They go on to state "Usually a continuity correction, by addition of 0.5, is considered for studies with zero counts in the estimation of the log of the odds ratio or the log of the risk ratio."

• M Subbiah and M R Srinivasan (2008) Classification of 2x2 sparse data sets with zero cells. Statistics & Probability Letters 78(18) 3212-3215.

A pdf copy of this paper is available to read and print from here.

On the use of the +0.5 smoothing for calculating the empirical logit transform see:

• David R COX and E J SNELL (1989) Analysis of Binary Data , Chapman and Hall: London

On the use of the +0.5 smoothing for calculating the d' signal detection parameter see:

• Michael J HAUTUS (1995) Corrections for extreme proportions and their biasing effects on estimated values in d'. Behavioral Research Methods, Instruments, & Computers, 27(1), 46-51.

See also

Signal Detection Parameters from SPSS There a different convention is followed of putting 1/2N and 1-1/2N in place of 0% and 100%.

here which suggests a nonparametric alternative to ROC curves which represents an average over all possible ROC curves. If this link is broken here are the details copied from there on how to compute ROC diagnostics using in R.

These pages are maintained by Ian Nimmo-Smith and Peter Watson

Last updated on 27 July, 2006