Measurement of family impact of skin disease: further validation of the Family Dermatology Life Quality Index (FDLQI)

Aim To adapt the Impact on Family scale (IOF), originally developed for families of children with chronic illnesses, for use in families of adult patients and to examine the convergent validity of the Family Dermatology Life Quality Index (FDLQI) by comparing it with the adapted version of the IOF scale. Methods Adult family members of patients with different skin diseases attending the out-patients clinic of a secondary referral centre completed the FDLQI and the adapted version of the IOF scale, whereas patients completed the Dermatology Life Quality Index (DLQI). Results A total of 50 patients and 50 family members/partners participated in the study. The mean scores for the three instruments were as follows: FDLQI = 6.0 (SD = 6.4, median = 4); IOF scale = 27.9 (SD = 8.2, median = 29); DLQI = 5.4 (SD = 5.6, median = 3). There was no difference between male and female participants in the mean scores of any of the three instruments. The FDLQI demonstrated high internal consistency (Cronbach's alpha = 0.91). Factor analysis revealed the presence of one factor structure underlying the items of the FDLQI, which explained 55.8% of the total variance. The IOF scale also showed a high internal consistency (Cronbach's alpha = 0.89). The results of factor analysis revealed one dominant factor and three weaker factors, which together explained 72% of the total variance. The convergent validity of the FDLQI was demonstrated by a highly significant positive correlation between the mean FDLQI and the IOF scale scores (r(s) = 0.61, P < 0.0001). All the items of the FDLQI also had significant correlations with the mean total IOF scale scores (P < 0.05). Conclusions The results of this study have demonstrated that with minor modifications IOF scale, which was originally developed for families of children suffering from chronic illnesses, can also be used in families of adult dermatology patients. The study has also provided further evidence of the validity of the newly developed FDLQI.