Predicting the risk of repetition after self harm: cohort study

Sir,

We read with interest the paper by Kapur et al about the ability of
psychiatrists and emergency physicians to predict the likelihood of repeat
episodes of self harm (1). As stated in the article the MASSH forms used
in the study gave the assessing physicians three options; high, moderate
or low risk. Despite these potential three outcomes the authors have
analysed the data in a dichotomous manner as either “high risk” or “not
high risk”. This may represent a difference in perspective between the
emergency physicians and the psychiatrists. From the Emergency Department
(ED) perspective we are most interested in identifying low risk patients
as these are a group who are perceived as not requiring immediate referral
to specialist services. A more logical analysis from the ED perspective
would be to classify patients as “low risk” vs “not low risk” i.e. the
high/moderate risk stratification would be combined as shown below.

Table 1: Predictive value of assessments (% (95% confidence 
interval))	

ED assessments	  vs      MH assessments

Sensitivity *:	82.5 (79.5 to 85.2) vs	69.9 (66.2 to 73.4)

Specificity #:	33.3 (32.9 to 33.6)vs	45 (44.4 to 45.5)

PPV ~:	        14.1 (13.6 to 14.5)vs	15.4 (14.6 to 16.2)

NPV ^:	        93.5 (92.4 to 94.5)vs	91.3 (90.2 to 92.3)

NNM £:	        43                   vs   23

* Sensitivity – if someone repeats self harm within 12 months, how
likely is he/she to have been identified as moderate or high risk at the
initial assessment.

# Specificity – If someone does not repeat self harm within 12
months, how likely is he/she to have been identified as at low risk at the
initial assessment.

~ Positive predictive value – what proportion of those identified as
moderate or high risk at then initial assessment actually go on to harm
themselves again within the next 12 months.

^ Negative predictive value – what proportion of those identified as
low risk would not go on to harm themselves again within the next 12
months.

£ Number needed to miss – how many patients need to be assessed before
one patient is labelled as low risk who is not.

Kapur et al did not report the negative predictive value, yet
arguably, it is clinically more relevant to the initial assessment than
the positive predictive value. Screening assessments should aspire to a
high sensitivity and high negative predictive values, not, as Kapur et al
seem to suggest, to a high positive predictive value.

These results suggest that there are indeed differences between
emergency department and mental health staff. Neither group performs well
at this level though on these figures for every 100 patients assessed; ED
staff would miss 2 patients who repeat whereas mental health staff would
miss 4. In our experience, ED assessments are usually rapid (usually
minutes) and integrated with clinical assessment of the severity of the
self harm. In contrast, assessment by mental health staff typically takes
much longer. It is therefore interesting to note that the increased time
does not improve the predictive nature of the assessment.

Simon Carley

Consultant in Emergency Medicine

Bernard Foëx

Consultant in Emergency Medicine and Critical Care

John Butler

Consultant in Emergency Medicine and Critical Care

On behalf of the Manchester Royal Infirmary emergency department
journal club.

1. Kapur N, Cooper J, Rodway C, Kelly J, Guthrie E, Mackway-Jones K.
Predicting the risk of repetition after self harm: cohort study. BMJ
2005;330:394-395

Competing interests:
None declared

Prognosis of behaviour is much more difficult than a clinical
prognosis.
Now and then studies and opinions on self- harm and suicide give rise to
endless and inconclusive discussions. In the context of prison inmates,
both waiting for the trial and convicted, the rate of self- harm and
suicide is much higher (about ten times) than in general population.
Reasons are often of a demonstrative nature, or the inmate wants to get
some benefit (for instance, to have a short holiday in a hospital, or to
obtain the detention at home). However, the prison population is not
representative of the general population. Risk assessment is a part of
clinical documents of the inmate, is classified as low, moderate and high,
and is based on clinical (psychological) conditions, anamnesis for self-
harm and drug abuse, familiar support and length of the detention. Self-
harm and suicide are more frequent among those waiting for the trial than
among convicted. In my opinion, this could be due to anxiety for a
verdict, capable of altering severely the future of the person. In any
case, a prognosis is practically impossible, but often the psychiatrist of
the prison, guilty of non- predicting a suicide, will face a trial for
culpable homicide.

Competing interests:
None declared