Table 1 Five approaches to presenting pooled PRO variables when primary studies have used different instruments to measure the same construct

(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

(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