Evidence-Based Medicine

etween – 1 and +1. When r is +1, there is a prefect positive relationship (when
one variable increases, so does the other, and the proportionate difference
remains constant). When r is –1 there is a perfect negative relationship (when
one variable increases the other decreases, or vice versa, and the proportionate
difference remains constant). This, however, does not rule out a relationship —
it just excludes a linear relationship.
Cost-Benefit Analysis
Converts effects into the same monetary terms as the costs and compares
them.
Cost-Effectiveness Analysis
Coverts effects into health terms and describes the costs for some additional
health gain (e.g. cost per additional MI prevented).
Cost-Utility analysis
Converts effects into personal preferences (or utilities) and describes how
much it costs for some additional quality gain (e.g. cost per additional quality
life-year, or QALY).
Crossover randomised trial
A trial in which participants receive one treatment and have outcomes measured,
and then receive an alternative treatment and have outcomes measured again.
The order of treatments is randomly assigned. Sometimes a period of no
treatment is used before the trial starts and in between the treatments (washout
periods) to minimise interference between the treatments (carry over effects).
Interpretation of the results from crossover randomised controlled trials (RCTs)
can be complex.
Crossover studies have the risk that the intervention may have an effect after
it has been withdrawn, either because the washout period is not long enough
or because of path dependency. A test for evidence of statistically significant
heterogeneity is not sufficient to exclude clinically important heterogeneity. An
effect may be important enough to affect the outcome but not large enough to
be significant.
Crossver Study Design
The administration of two or more experimental therapies one after the other in
a specified or random order to the dame group of patients.
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