Method of assessing involved facial areas: rule of fours

Summary Background  Disease extent or affected area is probably the most easily and most frequently measured index of patient disability in dermatological disorders such as psoriasis. However, no standard method is available for assessing involved facial areas. Objectives  To devise a method for assessing involved facial areas and to examine its validity and reliability. Methods  In study 1, the facial areas of 26 healthy adults were analysed and a new method for assessing facial areas was devised. In study 2, the validity and reliability of the devised method were investigated by 10 dermatologists using 30 photographs of patients with facial psoriasis. Results  In study 1, facial regions were defined to have percentage areas that were multiples of 4% of the total facial area (which we refer to as the rule of fours), i.e. forehead 24%, one cheek 20%, perioral area 8%, one aspect of an ear 4%, one periorbital area 4%, and nose 4%. In study 2, a comparison of values obtained using the rule of fours with those obtained using an image analysis system showed excellent intrarater and inter‐rater reliability when using the rule of fours. Conclusions  The rule of fours is useful for assessing involved facial areas. The application of this rule was found to provide an accurate and reliable method as compared with image analysis.