The estimation of prevalence of blindness by blind school survey in place of population-based survey would lead to:
Ans. c. There would be no differenceAccording to NAB (National Association for Blind), India Legal blindness is defined as visual acuity of not greater than 20/200 in the better eye with best correction or a visual field of less than 20 degrees.What does 20/200 means?A person with normal visual acuity can see an object clearly, at 200 feet; a legally blind person must be 20 feet or closer to see the same object.Note: 20/200 feet is same as 6/60 metersAccording to NPCB, the criteria for blindness (Economic Blindness) is visual acuity of <6/60 in the better eye with best possible correction.Thus, since both the criteria are same, the prevalence will remain same.
Over-estimate
Under-estimate
There would be no difference
Both of the methods are not to be used for this
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