What fraction of inmates have severe mental illness?

• A. 1/2
• B. 1/4
• C. 3/4 (72%)
• D. 1/6

Answer: (B)

The main idea here is how common serious mental illness is among people who are incarcerated. Inmates have a higher prevalence of serious mental illness than the general population, and a commonly cited estimate is about one in four inmates. So the option that reflects roughly twenty-five percent best matches the typical data, making it the best choice. The other numbers either imply a rate that’s much higher or much lower than what is usually observed in prison populations. For example, suggesting half or three-quarters would overstate how common SMI is, while one-sixth would understate it.