[no_gravity]

> At worst this is a 1% error rate

If those 1000 pairs of hairs really were from different, randomly choosen people. But we don't know the quality of that sample. Maybe the examiner looked at 1000 pairs of hairs, 10 looked similar to him and those 10 were from different heads, while the 990 that looked different were from the same head. That would give an error rate of 100%.

Even if we assume there were no errors in the sample, then we still don't know anything about the correlation between the judgement of the examiner and reality. Maybe he randomly considers one in 100 pairs of hairs to look similar. So while yes, the error rate would be 1%, his judgement would have absolutely no informative value. It would be as good as throwing dice.