An almost similar bias was found in the study conducted by Attaran et al. who reported that there is no significant correction between HB level and EPO level in anemic COPD patients, while their study didn’t measure the level of vitamin B12 and folate to exclude the combined anemia and so their results attributed the total anemic patients and low HB level to COPD conditions20. The gene discussed is EPO; the disease is anemia (phenotype).