The article explores some methodological and statistical problems and evaluates the validity of conclusions about the effects of administrative segregation from a 2000 research study conducted by researchers with the Correctional Service of Canada and Carleton University. The study was described as “the most comprehensive empirical review of the psychological effects of administrative segregation”. It acknowledged some limitations on their research, but the most critical are overlooked. In this article, attention is drawn to some of these problems. Some of the research problems identified are: sample size; prisoners’ previous experience in segregation; differential attrition rates (one experimental condition loses more subjects or loses them more quickly); attrition within the segregated sample; selection of dependent measures; and the power of the statistical tests. This article states that the psychological tests used in the research study had limits. Isolation, particularly repetitive isolation, may have subtle effects that cannot easily be captured by the current measures of psychological functioning. The following conclusion is drawn with the restrictions noted in the previous research study and those identified in this article the findings suggest that administrative segregation under two months in duration did not generate detectable psychological deterioration. Notes and References