How do I align outcome time points across trials before extracting data?

Build a time-point harmonisation table that lists every reported outcome time point per trial, maps each to the review's prespecified window, and records the chosen time point with a flag when the closest match falls outside the window.

Steps

1. Write the review's prespecified outcome windows first, before opening any trial report. Record each window as a defined interval (for example, a short-term and a longer-term window) so every later mapping has a fixed target. Result: a reference list of windows that does not shift as trials are added.
2. Extract every reported time point for the outcome from each trial, using the structured outcome fields in the trial's registration record and the reported results. ClinicalTrials.gov defines structured registration and results fields for outcomes and reported results, so use those fields to capture the time points the trial itself lists. Result: a per-trial list of reported time points.
3. Map each reported time point to the prespecified window it falls within, and mark the closest match for each trial. Result: one chosen time point per trial per window, with the mapping shown in the table.
4. Flag any trial whose closest match falls outside the window, and record the gap. Result: a visible set of out-of-window trials that you can handle consistently, for example by excluding them from that pooled analysis or reporting them separately.
5. Carry the chosen time point and its flag into the extraction form so the analysis stage uses the same mapping. Result: a documented link between the harmonisation table and the extracted data.

Why the table matters

Pooling outcomes measured at different times can mix effects from different follow-up periods. The Cochrane Handbook's meta-analysis guidance covers effect measures, heterogeneity, and sensitivity analyses, and a documented time-point mapping lets you test whether results change when out-of-window trials are handled differently. Keep the table alongside the extraction records so reviewers and readers can trace which time point each trial contributed.