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Evidence-Based Dermatology: Review
December 2000

Confounding and Interaction

Author Affiliations

DamianoAbeniMD, MPHMichaelBigbyMDPaoloPasquiniMD, MPHMoysesSzkloMD, MPH, DrPHHywelWilliamsPhD, FRCP

Arch Dermatol. 2000;136(12):1544-1546. doi:10.1001/archderm.136.12.1544

A report of a randomized clinical trial by Gallagher et al1 illustrates 2 important research concepts: confounding and interaction. In that trial, designed to evaluate the effectiveness of sunscreen in preventing development of new nevi, 458 children were randomly allocated to either a sunscreen or a control group. Parents of the children assigned to the intervention group (n = 222) were instructed to apply sun protection factor (SPF) 30 broad-spectrum sunscreen to the children's exposed skin when sun exposure was expected to last 30 minutes or longer. Parents of control children (n = 236) were given no advice regarding use of sunscreen. The number of new nevi that developed in 3 years was determined by doing nevus counts at baseline and at a 3-year follow-up visit.

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