Table 1.
Five approaches to presenting pooled PRO variables when primary studies have used different instruments to measure the same construct
| Approach | Description | Advantages | Disadvantages | Recommendation |
|---|---|---|---|---|
| (A) Standard deviation (SD) units (standardized mean difference; effect size) |
The pooled mean difference is presented in standard deviation units |
(+) Widely used |
(-) Interpretation challenging |
Consider complimenting other approaches with this; it is not recommended to use this approach independently. |
| (-) Misleading when trial SDs are heterogeneous | ||||
| (B) Natural units |
Linear transformation of trial data to most familiar scale |
(+) Easier to interpret if scale well-known |
(-) Few instruments in clinical practice are easy to interpret |
Approaches to conversion to natural units include those based on SD units and re-scaling approaches. We suggest the latter. In rare situations when instrument very familiar to front line clinicians seriously consider this presentation |
| (C) Relative and absolute dichotomized effects |
Obtain proportion above threshold in both groups and calculate relative or absolute binary effect measure |
(+) Very familiar to clinical audiences |
(-) Involve statistical assumptions that may be questionable |
If the minimal important difference is known use this strategy in preference to relying on SD units |
| Always seriously consider this option | ||||
| (D) Ratio of means |
The ratio between the mean responses in the intervention and control group |
(+) May be easily interpretable to clinical audience |
(-) Not applicable for change scores |
Consider as complementing other approaches, particularly the presentation of relative and absolute effects |
| (+) Fewer questionable assumptions |
(-) Interpretation requires knowledge of control group mean |
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| (E) Minimal important difference units | The pooled mean differences is presented in MID units | (+) May be easily interpretable to clinical audience | (-) Only applicable when minimally important difference is known | Consider as complementing other approaches, particularly the presentation of relative and absolute effects |