Elspeth Guthrie, George C Patton, Navneet Kapur, Kevin Mackway-Jones, Carolyn Chew-Graham, James Moorey et al
Guthrie E, Patton G C, Kapur N, Mackway-Jones K, Chew-Graham C, Moorey J et al.
Randomised controlled trial of brief psychological intervention after deliberate self poisoningCommentary: Another kind of talk that works?
BMJ 2001; 323 :135
doi:10.1136/bmj.323.7305.135
Pragmatic trial causes disappointment
EDITOR-
The article by Guthrie et al presents an exemplary evaluation of the
role of a brief psychodynamic intervention in the management of deliberate
self poisoning. The trial is described as a pragmatic one, with the
effects of the psychodynamic intervention being compared to usual
treatment. The authors acknowledge that such a comparison may bias the
results due to an effect of the increased contact with nurse therapists in
the intervention group which is not related to the intervention itself. I
would like to suggest a further potential source of bias: disappointment
in the usual treatment group at not being randomised to the new treatment
programme. Following a detailed description of the trial and the new
treatment programme, those participants randomised to the control group
are told they cannot receive the new treatment and are sent back to the
usual care services. 62% of those randomised to the usual care group had a
history of deliberate self harm and are likely to have had previous, and
at least partly unsuccessful, contact with those services. The effect of
the randomisation on the control group can only be surmised, but
disappointment and a consequent negative effect on the self report
measures is certainly possible. If this was the case then the study has
failed to give us a pragmatic estimate of the effect of the intervention;
the estimate has become contaminated by the research process. It would be
interesting to know whether the baseline evaluation was completed before
or after the participants learnt the outcome of the randomisation.
A second difficulty in interpretation is not discussed by Guthrie et
al. Strong evidence of a reduction in suicidal ideation is obtained for
the six month assessment but not for the earlier end of treatment
assessment. It is feasible that the beneficial effects of the intervention
increased and were not merely maintained during the six month follow up
period. This would be a distinctly unusual outcome however, and such a
temporal pattern of effect was not hypothesised. In fact without such a
hypothesis it may have been more appropriate to conduct a single
significance test for each of the two self report scales in turn, with
post-treatment data consisting of a single mean of the post-treatment
assessments for each patient.
Interpretation of the results would have been assisted by the
provision of further information. Firstly, 60% of the intervention group
completed the intervention programme. Can a particularly strong effect of
the intervention be demonstrated for these individuals, otherwise there is
a leap of faith in allocating the observed difference between randomised
groups to the treatment itself. Secondly, baseline means for those people
completing the six month assessment, presented separately for the two
treatment groups, would have assisted in the interpretation of the
covariance analysis of the two self report measures.
The points give further cause for Guthrie et al's own cautious
interpretation. However, to end on a positive note, this study provides
the motivation, and a great deal of useful information, for further
research.
One final point: is the standard deviation of age really 1.5 years?
Competing interests: No competing interests