SAMPLING BIAS, SAMPLE SIZE, ORDINAL REGRESSION MODEL, AND COMPETING RISK IN EVALUATING ASSOCIATION BETWEEN ABO BLOOD GROUP AND SEVERITY OF LIVER FIBROSIS IN HEPATITIS C VIRUS PATIENTS (LETTER TO EDITOR)

摘要

Sir,I read with interest the paper by Shavakhi A et al., about association between severity of fi brosis in Hepatitis C virus (HCV) patients and ABO blood group.[1] According to the only meta-analysis of the prevalence of HCV, total prevalence in general population of Iran is 0.16%.[2] There are some sources for sampling bias. Authors did not include those who had received anti- HCV treatments. By excluding cases who were treated for HCV, we are excluding more severe cases and may underestimate the association between severity of liver fi brosis in HCV patients and blood group. I was interested to know if is there any change in severity of this association if we consider the situation of these cases before their enrollment in the treatment and include them in analysis? On the other hand, the probability of selecting more severe cases increases when patients are selected from University clinics in comparison with private clinics.