Mechanisms and Extrapolation in the Abortion-Crime Controversy - Mechanism and Causality in Biology and Economics - page 176

Chapter 10
Mechanisms and Extrapolation
in the Abortion-Crime Controversy
Daniel Steel
Abstract John Donohue and Steven Levitt's seminal and controversial article, The
Impact of Legalized Abortion on Crime , famously argues that the legalization of
abortion in 1973 in the Unites States is a significant factor explaining the surprising
decline in crime rates that occurred there in the 1990s. In this chapter, I examine the
role of extrapolation in Donohue and Levitt's study and draw three main philosoph-
ical conclusions. First, several different types of causal claims might be at issue in
an extrapolation—including claims about mechanisms and probabilistic causal
effects—and these distinctions matter for methodology because different
conditions may be required to support extrapolation in each case. Secondly, scien-
tific study of a phenomenon typically generates evidence at a variety of levels of
aggregation, and this has important implications for extrapolation. The third and
final point follows on the heels of the second. Like almost all other scientific
inferences, extrapolations are normally components of a complex web of interre-
lated evidence that must be considered together in assessing a hypothesis.
John Donohue and Steven Levitt's ( 2001 ) seminal and controversial article, The
Impact of Legalized Abortion on Crime , famously argues that the legalization of
abortion in 1973 in the Unites States is a significant factor explaining the surprising
decline in crime rates that occurred there in the 1990s. Their argument is interesting
from a philosophical perspective for a number of reasons, one of which is its use of
a variety of methodological approaches in building a case for a causal claim.
Although most of the debate surrounding Donohue and Levitt's hypothesis has
focused on the interpretation of the statistical data, an important part of their case
involves tracing a mechanism whereby legalization of abortion could reduce crime
rates. The central idea is that unwanted children—whose births were likely to have
D. Steel ( * )
Department of Philosophy, Michigan State University, 503 South Kedzie Hall,
368 Farm Lane, East Lansing, MI 48824-1032, USA
e-mail: [e-mail]