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Centre for Evidence-
Based Medicine

Completed Therapy Worksheet for Evidence-Based Mental Health


Susser E, Valencia E, Conover S, et al. Preventing recurrent homelessness among mentally ill men: a 'critical time' intervention after discharge from a shelter. Am J Public Health 1997 Feb; 87: 256-62.

Are the results of this single preventive or therapeutic trial valid?

  1. Was the assignment of patients to treatments randomised?
    And was the randomisation list concealed?
    Yes, but there is no mention of the method of concealment of allocation
  2. Were all patients who entered the trial accounted for at its conclusion?
    And were they analysed in the groups to which they were randomised?
    Yes - two usual care participants were lost to follow-up but they were rated as being free from homelessness during the follow-up period - this would produce a conservative estimate of the relative effectiveness of the "critical time" intervention
  3. Were patients and clinicians kept "blind" to which treatment was being received?
    No - this was impractical due to the nature of the interventions
  4. Aside from the experimental treatment, were the groups treated equally? Hard to say from the paper
    Were the groups similar at the start of the trial? Yes - although there may have been slightly more cocaine dependence and less lifetime homelessness in the usual services only group

Are the valid results of this randomised trial important?

Sample Calculations

More than 54 nights of homelessness Relative Risk Reduction (RRR) Absolute Risk Reduction (ARR) Number Needed to Treat (NNT)
Usual services only
Control Event Rate (CER)
"Critical time" Intervention
Experimental Event Rate (EER)
40% 21% (40%-21%)/40%
= 47%
40% - 21%
= 19%
= 5 pts

95% Confidence Interval (CI) on an NNT = 1 / (limits on the CI of its ARR)
= +-1.96 sqrt(((CERx(1-CER))/(# of control pts.)) + ((EERx(1-EER))/(# of exper. pts.)))
= +-1.96 sqrt(((0.40x0.60)/48) + ((0.21x0.79)/48))
= ±18%

Can you apply this valid, important evidence about a treatment in caring for your patient?

Do these results apply to your patient?

  1. Are your patients so different from those in the trial that its results can't help you?
    No, they are similar to those included in the trial - although there might be differences between the US and elsewhere

How great would the potential benefit of therapy actually be for your individual patient?

  1. Method I: f
    Risk of the outcome in your patient, relative to patients in the trial. expressed as a decimal: 1.0

    NNT/F = 5/1 = 5
    (NNT for patients like yours)
  2. Method II: 1 / (PEER x RRR)
    Your patient's expected event rate if they received the control treatment: PEER:______

    1 / (PEER x RRR)
    = 1/________
    = __________
    (NNT for patients like yours)

Are your patient's values and preferences satisfied by the regimen and its consequences?

  1. Do your patient and you have a clear assessment of their values and preferences?
    Needs to be assessed in each patient
  2. Are they met by this regimen and its consequences?
    Needs to be assessed in each patient

Additional Notes


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