With simple probability, using their 0.4%, it means that you would expect 0.26 blind child out of 66 to have schizophrenia. So that they see 0 is perfectly reasonable. For the other psychotic illness, that probability is 1.5%. So, out of 66 you would have expected 0.99. Maybe that kid is the lot and will develop apparent symptoms of psychosis in the next few years...
In general, an epidemiology study without statistic means that they try to find something but they didn't and couldn't explain why.
Now, common epidemiology statistic are going to use a 5% alpha error and a 95% confidence. So, if they were to repeat that experiment a 100 times, 95 times you would observe a value close to the mean. The probability numbers given are maximum, and I would guess that the minimum is zero. So 95% of the time, you would have a value much lower, and closer to zero individuals out 66 for psychosis.
With simple probability, using their 0.4%, it means that you would expect 0.26 blind child out of 66 to have schizophrenia. So that they see 0 is perfectly reasonable. For the other psychotic illness, that probability is 1.5%. So, out of 66 you would have expected 0.99. Maybe that kid is the lot and will develop apparent symptoms of psychosis in the next few years...
In general, an epidemiology study without statistic means that they try to find something but they didn't and couldn't explain why.
Now, common epidemiology statistic are going to use a 5% alpha error and a 95% confidence. So, if they were to repeat that experiment a 100 times, 95 times you would observe a value close to the mean. The probability numbers given are maximum, and I would guess that the minimum is zero. So 95% of the time, you would have a value much lower, and closer to zero individuals out 66 for psychosis.