[Sampling survey of mentally deficient people in Sichuan]

From first April to 15th May 1987, 145,201 people were investigated by using the ways of layer, equal probability and mass sampling. Two thousand three hundred and forty two of them were confirmed to be mentally deficient. The incidence was 16.13%. It was estimated that 1,665,000 people have mental deficiency in Sichuan. The estimated range of reliability of 95% was 1,528,000-1,801,000. One million and three hundred ninety three thousand of them only had mental deficiency, while 272,000 had other organic deficiency. Male:female ratio was 101.4:100. The incidence of 6-14 year-old was 38.14%, which was 3 times higher than that of other age groups. Mild mental deficiency was 16.4 times more than severe mental deficiency. The most common causes were hereditary diseases, encephalitis, malnutrition, cerebral trauma, pregnant diseases, etc. All of the causes belonged to preventable diseases.