By Tapio Lappi-Seppälä

Over the last 15 years imprisonment rates have declined in Europe on average by 15 percent and in the United States by 30 percent. Does this imply that, after decades long prison growth, we are facing a period of penal moderation? Since crime has also decreased, any assessments of a “moderate turn” are premature without considering how much of this decline is just a consequence of declining crime. This article begins to answer these questions first by examining previous attempts to measure the impact of crime on prison populations. To obtain a more precise view of the causal mechanisms, and to overcome some of the controversies in earlier research, a distinction between volume effects and policy effects is introduced. Empirical analyses are reported using two samples. The long-term sample from the 1960s onwards exemplifies the diversity of penal responses and differing prison trends during the times of increased crime in nine Western countries. Comparisons with 35 European countries from 2008 to 2024 show that prison populations followed declining crime quite closely. The answer to the initial question remains negative: There are ever more prisoners relative to recorded crime and convictions, suggesting a lower custody threshold than before. The number of admissions has declined, but the average length of prison terms has grown in almost all European countries. Despite the nominal decline of prison populations there is no indication that European penal policy is shifting toward leniency.

Crim Law Forum 36, 269–305 (2025).