Comment on: Quality of Life and Psychological Morbidity in Vitiligo Patients: A Study in a Teaching Hospital from North-East India.

Sir,

Went through with interest article entitled “Quality of life and psychological morbidity in vitiligo patients: A study in a teaching hospital from North-East India” published in Indian J Dermatol (2015;60:142-6).[1] This study was conducted in a case-control design mode with the aim to assess the impact of the disease on the quality of life of patients suffering from vitiligo and also to ascertain any psychological morbidity like depression associated with the disease and to compare the results with that of healthy control group.[1] The authors deserve credit for their effort for highlighting an important issue of psychological morbidity in a condition like vitiligo. However, I have some concerns with the methodology adopted for the purpose of this study.

As per the authors, clinically diagnosed vitiligo patients in the age group of 18–40 willing to take part in the study were included as cases and the control group for these included age-matched healthy medical and paramedical workers.[1] The authors further state that 100 vitiligo patients of the age range 18–40 and 50 ages-matched healthy controls participated in the study. This brings me to my concerns with this study.

The authors in this study have used a smaller number of controls for cases, which may not provide adequate power to the conclusion drawn from the study sample. Agreed that the study being a hospital based case-control study, choosing suitable hospital controls is often difficult. However, after the cases and controls for a study have been determined, it is necessary to decide how many controls per case should be selected. When the number of available cases and controls is large, and the cost of obtaining information from both groups is comparable, the optimal control to case ratio is 1:1.[2] The greater the number of controls per case, the greater the power of the study (for a given number of cases). However, there is generally little justification to increase this ratio beyond 4:1.

Importantly, the authors claim that age- and sex-matched controls without vitiligo were used in this study. However, it does not seem that the authors have age- and sex-matched. If, cases and controls were individually matched on age and sex, then the number of cases and controls would have been equal and unequal. Age and sex matching of controls mean a similar proportion to the cases fall into the various categories defined by the matching variable (sex and age in this study). For instance, if 25% of the cases are males aged 65–75 years, 25% of the controls would be taken to have similar characteristics. Now, if the authors would have age- and sex-matched, then the number of cases and controls would have been equal (100 cases to 100 controls) and not unequal (100 cases to 50 controls) as is the cases in this study.