Select Committee on Science and Technology Written Evidence

Memorandum 57

Supplementary evidence from Dr James Trussell, Dr Kate Guthrie and Dr Sam Rowlands


  The evidence submitted to the Select Committee on Science and Technology by Professor Patricia Casey cannot possibly inform anyone about the effect of induced abortion on the subsequent mental health of the woman. To understand why, it is helpful to consider the ideal research design to answer this question. In that ideal research design, women wishing to terminate their pregnancies would be randomly assigned to receive a termination or have their request denied without the possibility of their having a termination elsewhere, as alluded to by Dr Rowlands in his oral evidence at Question 83. Of course, no study has employed this design; it is unlikely that such a trial will ever be undertaken. The research design that is farthest from the ideal is one in which women obtaining terminations are compared with women who got pregnant because they wanted to become mothers. These simply are not comparable groups because it is not only the abortion itself that differentiates them. They are undoubtedly different in many ways (since one group wanted to have a baby whereas the other did not), only some of which are observable. So no matter how many other factors are controlled in the statistical analysis (such as past mental health), this design cannot be made to mimic random assignment. The design that is next farthest from the ideal would compare women obtaining terminations with all women giving birth, some of whose births would be unintended; this is the design of the New Zealand study by Fergusson et al so highly praised by Casey.

  The design closest to the ideal would be to compare women obtaining terminations with women whose request for a termination was denied. Note that women are not randomly assigned at all because some have their request denied. Presumably their reasons for wanting a termination were not so compelling, so perhaps they are "healthier" on average. The UK study by Gilchrist et al is the only study with this design, and it found that the two groups had identical rates of subsequent psychiatric illness, psychotic illness, and deliberate self harm. The design of the Gilchrist study is weakened by the fact that women in each of the groups may have had prior induced abortions. The data were indirectly standardised for age, marital status, smoking habit, age at leaving full-time education, gravidity and previous history of induced abortion at recruitment, since the comparison groups differed on those characteristics (data available from the authors). The authors also acknowledge that the study had little power to detect important effects occurring in the denied abortion and changed-their-mind groups because there were too few women in these groups.

  Casey cites only studies like the one from New Zealand, all of which have the fatally flawed research design identified above. Even if past and subsequent mental health is measured perfectly, the flawed research design means that the results cannot possibly be informative about whether induced abortion is causally related to subsequent mental health. Casey's evidence therefore does not answer this fundamental question and her review of recent studies does not give the Committee any new insight.


Fergusson D M, Horwood L J, Ridder E M. Abortion in young women and subsequent mental health. J Child Psychol Psychiatry 2006 Jan;47(1): 16-24.

Gilchrist A C, Hannaford P C, Frank P, Kay C R. Termination of pregnancy and psychiatric morbidity. Br J Psychiatry 1995 Aug;167(2): 243-8.

October 2007

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