Measurement properties of Skindex-16: a brief quality-of-life measure for patients with skin diseases.
BACKGROUND
An accurate, sensitive, but brief quality-of-life outcomes measure is needed for studies of dermatologic care.


OBJECTIVE
To construct a single-page version of Skindex (a dermatologic quality-of-life instrument) that would have two new features compared with the current 29-item version: (1) fewer items to which a majority of patients choose the same response, and (2) measurement of bother rather than frequency of patient experiences.


METHODS
Random samples of patients waiting for dermatology appointments in clinics of Veterans Affairs hospitals and in private dermatology practices completed questionnaires; 692 patients responded to the parent instrument and 541 additional patients responded to the brief version. Reproducibility, internal consistency reliability, validity, and responsiveness of the brief version of Skindex were determined.


RESULTS
For 16 items of the current 29-item version (55%), more than 50% of patients responded "Never." After an explicit process of item analysis and elimination, a single-page 16-item version was composed that asks patients about bother from their experiences; responses are reported as three scales, Symptoms, Emotions, and Functioning. For 6 items of the 16-item version (38%), more than 50% of patients responded "Never." Scale scores were reproducible after 72 hours (r = 0.88-0.90) and were internally reliable (Cronbach's alpha = 0.86-0.93). The instrument demonstrated both content and construct validity: Most patients' responses to an open-ended question about their skin disease was addressed by the items; patients with inflammatory dermatoses had higher scores than those with isolated lesions; and in an exploratory principal axes factor analysis with an oblique rotation, 74% of the common variance was explained by three factors that correlated with the a priori scales. Mean scale scores stayed the same or changed in the expected direction in patients who reported that their skin was the same or had improved.


CONCLUSIONS
This brief single-page version of Skindex accurately and sensitively measures how much patients are bothered by their skin conditions.
Chren
M M
MM
Department of Dermatology, University of California at San Francisco, San Francisco, California, USA. mmchren@itsa.ucsf.edu
Lasek
R J
RJ
Sahay
A P
AP
Sands
L P
LP
D000203:Activities of Daily Living; D000704:Analysis of Variance; D001294:Attitude to Health; D004644:Emotions; D005163:Factor Analysis, Statistical; D006801:Humans; D011594:Psychometrics; D011788:Quality of Life; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index; D012871:Skin Diseases / Q000145:classification* / Q000523:psychology*; D012919:Social Behavior; D011795:Surveys and Questionnaires / Q000592:standards*