Cochrane Database of Systematic Reviews (CDSR)

Tags:meta analysisdatabaseprimary outcomeRCTHover over the tag text for details.
Domainmedicine & health
Data90k studies in 6.6k Cochrane reviews
Note

To download only this data file: Cochrane.rds (37 MB)

To download all BEAR datasets, click here.

Description

Trials with results available in CDSR, https://www.cochranelibrary.com/ (Cochrane Collaboration 2025).

Snapshot date: 20 November 2025

Data collection: Using the R package cochrane (Schwab 2024), we combined data from 8,726 CDSR review records into a single file, cdsr_interventions_19nov2025.csv (63 MB).

Data processing: We applied several processing steps and extensive filtering.

During processing, we cleaned up study years and categorised measures (risk ratio, odds ratio, mean difference, etc.) and experimental designs. In particular, we created an “RCT” flag by scanning each review abstract for its inclusion criteria. Most studies in CDSR are RCTs, but some reviews also allowed quasi-experimental studies, so we could not classify many studies. We also classify outcome rows into efficacy, safety, dropouts, and bias based on the comparison, outcome, and subgroup labels.

To calculate effect sizes and z-values for BEAR, we used metafor to calculate standardised mean differences for continuous outcomes and probit-transformed differences for dichotomous outcomes. This puts continuous and binary outcomes on a comparable scale.

Unlike in most of the other datasets in BEAR, we filter CDSR data heavily. There are six important decisions:

  1. Use only the outcome and comparison from each review coded as “1”, as these are most likely to be the primary outcome and most relevant comparison.
  2. Keep only rows classified as efficacy, excluding likely safety, dropout, and bias-related outcomes based on comparison, outcome, and subgroup labels.
  3. Use only studies with continuous and dichotomous outcomes, removing rows where effect estimates are based on instrumental variables or individual patient data.
  4. Remove rows where the effect measure is unknown (keeping OR, RR, Peto OR, mean difference, standardised mean difference, and risk difference) and rows with no participants.
  5. Remove count data with no events or a 100% event rate in both arms (see the discussion of zero-event studies).
  6. Exclude reviews marked as withdrawn in the source RM5 file.

These processing steps are applied in the main dataset, BEAR.rds. Additional rows are still available to researchers in the individual dataset, Cochrane.rds. That file retains withdrawn reviews with a withdrawn indicator (1 for withdrawn, 0 otherwise). We also determined review DOIs from either the saved file or a further search (for reviews that had multiple editions).

As a result, the distributed BEAR.rds file includes a smaller analysis subset with about 33,500 rows: the first comparison and first outcome from each review, restricted to efficacy outcomes. The processed data/Cochrane.rds file is larger and is available for users who want to make different selection decisions. It contains 760,486 result rows, representing 90,042 review-study pairs across 6,619 Cochrane reviews.

A large proportion of CDSR rows have binary outcomes with no events in either arm or events in all participants in both arms. In the BEAR analysis subset before this exclusion, 2,327 of 24,959 binary rows (9.3%) met one of these conditions: 2,208 rows (8.8%) had no events in either arm and 119 rows (0.5%) had all participants experiencing the event in both arms.

Zero-event studies may be important for some metascientific analyses, but for modelling the distribution of z-values they are unhelpful. With these rows included, the empirical distribution has extra observations at or near zero, and the normal approximation is poor. Because of this peak at zero, including these non-significant studies has the counter-intuitive effect of increasing the estimated degree of selection: the fitted distribution has a steeper drop-off between zero and the conventional significance threshold at 1.96.

Study characteristics:

  • Sample size and year: ss is the sum of the two arm totals; year is study.year.

  • Study ID: we use study.name.

  • Meta-analysis ID: we use the Cochrane review identifier (id). Refer to doi_meta for DOI identifiers of reviews.

  • Topic: we use the Cochrane specialty.

  • subset records study-data provenance: published, unpublished, sought or mixed.

  • method: We review meta-analysis eligibility criteria to determine which meta-analyses included only randomised trials. This classifies 67% of estimates as RCTs; the remaining 33% could not be classified reliably, although many are likely to be RCTs because Cochrane meta-analyses typically include RCT or quasi-randomised evidence.

  • measure: About 32% of estimates are standardised mean differences and 68% are differences between probit-transformed event proportions.

  • topic is Cochrane specialty and subset is source data type (published, unpublished, sought, or mixed); outcome_group is also available in the processed data.

Model of z-values

Characteristic Estimate
Probability of significance 28%
Relative probability of publication for |z| < 1.96 0.82
Successful replication for |z| > 1.96 60%
Correct sign for |z| > 1.96 97%
What do these terms mean?
Probability of significance
The reported value is the assurance: the proportion of significant results adjusted for publication bias.
Relative probability of publication
The relative probability of observing a result below the |z| = 1.96 threshold rather than above it. Values below one indicate lower observation probability below the conventional two-sided significance threshold.
Successful replication
The probability that an exact replication has the same sign and a |z| greater than 1.96, conditional on the original result having |z| greater than 1.96.
Correct sign
The probability that the observed effect has the same direction as the true effect, conditional on an original result with |z| greater than 1.96.

Cochrane Database of: Systematic Reviews mixture model plot

Data dictionary

One row is one study result within a Cochrane review analysis. Summaries count rows, not distinct reviews.

Review identifiers

Variable Definition Summary
cochrane_id Cochrane review identifier.
doi_meta DOI of the review.
withdrawn Whether the review was withdrawn. 0 733,563 / 760,486 (96.5%); 1 26,923 / 760,486 (3.5%)

Review characteristics

Variable Definition Summary
specialty Cochrane specialty / review group. Pregnancy and Childbirth 66,114 / 760,486 (8.7%); Hepato-Biliary 52,397 / 760,486 (6.9%); Heart 41,515 / 760,486 (5.5%); Common Mental Disorders 40,320 / 760,486 (5.3%); Airways 35,504 / 760,486 (4.7%); remaining 524,636 / 760,486 (69.0%); missing 0 / 760,486 (0.0%)
rct Whether review eligibility criteria indicate RCTs only. TRUE 544,731 / 760,486 (71.6%); FALSE 215,755 / 760,486 (28.4%)
id Cochrane review identifier supplied by the RM5 parser.

Analysis identifiers

Variable Definition Summary
comparison.nr Comparison number within the review.
comparison.name Comparison label.
comparison.id Cochrane internal identifier for the comparison.
outcome.nr Outcome number within the comparison.
outcome.name Outcome label.
outcome.measure Effect measure reported by Cochrane.
outcome.id Cochrane internal identifier for the outcome.
outcome.flag Cochrane outcome type. DICH 510,861 / 760,486 (67.2%); CONT 249,625 / 760,486 (32.8%)
subgroup.nr Subgroup number within the outcome.
subgroup.name Subgroup label.
subgroup.id Cochrane internal identifier for the subgroup. missing 248,547

Study characteristics

Variable Definition Summary
study.id Cochrane internal identifier for the study. BEAR uses study.name as the study identifier.
study.name Study label; used as studyid in BEAR.
study.year Study year inferred from the Cochrane year field or study label. missing 27,883
study.data_source Source of the study data: published only (PUB), unpublished only (UNPUB), published with unpublished data sought but not used (SOUGHT), or a mixture of published and unpublished data (MIX). PUB 630,749 / 760,486 (82.9%); MIX 101,642 / 760,486 (13.4%); SOUGHT 17,328 / 760,486 (2.3%); UNPUB 10,767 / 760,486 (1.4%)

Reported effects

Variable Definition Summary
effect.size Effect estimate reported by Cochrane.
se Reported standard error.
ci.lower Reported lower confidence limit.
ci.upper Reported upper confidence limit.

Arm inputs

Variable Definition Summary
events1 Event count in the treatment/experimental arm for binary outcomes.
total1 Participant count in the treatment/experimental arm.
mean1 Mean in the treatment/experimental arm for continuous outcomes.
sd1 Standard deviation in the treatment/experimental arm.
events2 Event count in the control/comparator arm for binary outcomes.
total2 Participant count in the control/comparator arm.
mean2 Mean in the control/comparator arm for continuous outcomes.
sd2 Standard deviation in the control/comparator arm.

BEAR calculations

Variable Definition Summary
measure_group Cochrane effect measure, standardised to RR, OR, PETO_OR, RD, MD, or SMD. RR 397,896 / 760,486 (52.3%); MD 179,356 / 760,486 (23.6%); OR 77,446 / 760,486 (10.2%); SMD 70,269 / 760,486 (9.2%); PETO_OR 23,480 / 760,486 (3.1%); RD 12,039 / 760,486 (1.6%)
measure Effect measure used by BEAR: SMD for continuous outcomes or probit difference for binary outcomes. probit 510,861 / 760,486 (67.2%); SMD 249,625 / 760,486 (32.8%)
measure_detailed Detailed label for the BEAR effect measure. probit 510,861 / 760,486 (67.2%); SMD (Hedges’ g) 249,625 / 760,486 (32.8%)
outcome_group Outcome category derived from comparison, outcome, and subgroup labels: efficacy, safety, dropouts, or bias. efficacy 595,500 / 760,486 (78.3%); safety 100,241 / 760,486 (13.2%); bias 46,480 / 760,486 (6.1%); dropouts 18,265 / 760,486 (2.4%)

References

Cochrane Collaboration. 2025. Cochrane Database of Systematic Reviews. https://www.cochranelibrary.com/cdsr.
Schwab, Simon. 2024. Cochrane: Import Data from the Cochrane Database of Systematic Reviews (CDSR). https://github.com/schw4b/cochrane.