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Centre for Evidence-
Based Medicine

Completed Therapy Worksheet for Evidence-Based Purchasing


Rosler M, Anand R, Cicin-Sain A, Gauthier S et al. Efficacy and safety of rivastigmine in patients with Alzheimer's Disease: international randomised controlled trial. BMJ 1999;318:633-40.

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. Randomisation was generated by a computer. It is not explicitly stated, but reasonable to assume that this code was kept from investigators (p.634)
  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. Figure 1, page 635. The authors used intention-to-treat analysis.
  3. Were patients and clinicians kept "blind" to which treatment was being received?
    Yes. The treatment (low and high dose) and placebo drug capsules were identical, and patients took the same number of capsules, irrespective of dose.
  4. Aside from the experimental treatment, were the groups treated equally?
  5. Were the groups similar at the start of the trial?
    Apparently the groups were comparable (results, page 365), although there is no table or published data to demonstrate demographic characteristics here. Table 2 shows that baseline scores were similar for both groups. There were more women than men (59% vs. 41%) in the whole study.

Are the valid results of this randomised trial important?

Your Calculations

4+ point improvement on Alzheimer's disease assessment scale* using intention-to-treat analysis Relative Benefit Increase
Absolute Benefit Increase
Number Needed to Treat
High dose Low dose Placebo (EER - CER)/CER EER - CER 1/ABI
24% 15% 16% high vs. placebo (24%-16%)/16%
= 50%
24% - 16%
= 8%
= 13 pts
low vs. placebo (15%-16%)/16%
= 63%
= -1%
(or, 1% without the minus sign for an Absolute Risk Increase)
= 100 pts
(i.e. an NNH)
* Note that it is possible to calculate these figures for any of the five outcomes cited in Table 3, using any of the three forms of analysis given, if learners are interested.
** Because the outcome is beneficial, rather than harmful, it makes more sense in this case to use the term "relative benefit increase" rather than "relative risk reduction".

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(((0.096x0.904)/730) + ((0.028x0.972)/711))
= ±2.4%

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

Do these results apply to your patient?

  1. Is your patient so different from those in the trial that its results can't help you?
    Maybe. Depends upon patient type - those in this trial were mild to moderately severe patients, including mainly women and white people. Also, it depends upon how clinically relevant you feel the "4+ point improvement" on the Alzheimer's scale is.

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

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

    NNT/f = __________
    (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?
    Need to ascertain from group
  2. Are they met by this regimen and its consequences?
    Need to ascertain from group and decision about clinical relevance of the trial's findings

Additional Notes


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