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Centre for Evidence-
Based Medicine

Completed Prognosis Worksheet for Evidence-Based Mental Health

Citation

Wiersma, D, Nienhuis, FJ, Slooff, C.J. and Giel R. Natural course of schizophrenic disorders: a 15-year followup of a Dutch incidence cohort. Schizophr.Bull. 24 (1):75-85, 1998.

Are the results of this prognosis study valid?

  1. Was a defined, representative sample of patients assembled at a common (usually early) point in the course of their disease?
    Yes - all patients in a circumscribed geographical region were included after the onset of their first ever episode of illness.
  2. Was patient follow-up sufficiently long and complete?
    Yes- up to 15 years
  3. Were objective outcome criteria applied in a "blind" fashion?
    Standard instruments were used with clear definitions of relapse although it is not clear that the follow-up was performed blind to baseline information
  4. If subgroups with different prognoses are identified, was there adjustment for important prognostic factors?
    Looked at a number of possible predictors of first relapse.
  5. Was there validation in an independent group ("test-set") of patients?
    No

Are the valid results of this prognosis study important?

  1. How likely are the outcomes over time?
    After 15 years, 15% of patients had experienced no further psychotic episodes
  2. How precise are the prognostic estimates?
    95% confidence interval - 7% to 22%

If you want to calculate a Confidence Interval around the measure of Prognosis

Clinical Measure Standard Error (SE) Typical calculation of CI
Proportion (as in the rate of some prognostic event, etc) where:

the number of patients = n

the proportion of these patients who experience the event = p
sqrt((px(1-p))/n)
where p is proportion and n is number of patients
If p = 12/82 = 0.15 (or 15%) and n=82
SE = sqrt((0.4x(1-0.4))/60)
= 0.039 (or 3.9%)

95% CI is 15% ±1.96 x 3,9% or 7% to 22%

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

Do these results apply to your patient?

  1. Were the study patients similar to your own?
    Yes
  2. Will this evidence make a clinically important impact on your conclusions about what to offer or tell your patient?
    Yes

Additional Notes

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