The accuracy of biometric identification depends on the chance of a false positive: the probability that the identifiers of two persons will match. Individuals whose identifiers match might be termed duplicands. When very many people are to be identified success can be measured by the (low) proportion of duplicands. The Government of India is engaged upon biometrically identifying the entire population of India. An experiment performed at an early stage of the programme has allowed us to estimate the chance of a false positive: and from that to estimate the proportion of duplicands. For the current population of 1.2 billion the expected proportion of duplicands is 1/121, a ratio which is far too high.
