Melanocytic nevi in children. II. Observer variation in counting nevi

A survey of benign melanocytic nevi was conducted among children in Perth, Western Australia, in 1985. Children were examined by one of a team of five nurses who counted all of their nevi. Linear regression was performed on the logarithmically transformed mole counts to assess the degree of interobserver variation. Among 2,354 white children aged 5-14 years, 3.9% of the variation in numbers of nevi of all sizes and 7.7% of the variation in nevi 2 mm or more in diameter was attributed to variation among observers. The observer variation was less for the back than for any other body site. Differences between observers were greater in children with heavy freckling than in children with little or no freckling. However, the interaction between degree of freckling and observer accounted for more than 1% of the variation in counts only at sites where freckling was common (the face and neck and the upper limbs). The reproducibility of counts made by pairs of observers on 236 of the children, estimated by intraclass correlation coefficients, was 0.79 for all nevi and 0.65 for nevi 2 mm or more in diameter. The mean count of nevi on the back obtained by examining photographs of 100 children aged 8-9 years (11.9 nevi) was similar to that recorded by the examiners (12.3; p = 0.31), and the two measures were highly correlated (r = 0.89).