Objective: To assess the impact of search strategies for a different language on systematic review results, using English index searches versus Chinese index searches for Chinese literature pertaining to cerebral palsy (CP) as an example.
Methods: We conducted two parallel searches with the same search strategy. Both searches looked for studies published in the Chinese language that examined risk factors for CP. The first was conducted in standard English indexes and the second was in standard Chinese indexes. We compared the results using the two searches using a Z-test. Egger's test and Begg's test were used to assess the potential publication bias.
Results: Using the English indexes, nine studies were identified. Using the identical search and inclusion/exclusion criteria in the Chinese indexes, 17 studies were returned. The association between intracranial hemorrhage and CP was much stronger in the studies found in the search by the English indexes (odds ratio [OR] 61.73, 95% confidence interval (CI) 19.48-195.61) than the results from studies identified by the Chinese indexes (OR 9.57, 95% CI 2.42-37.88). The association between hypertension and CP was not significant in studies found using the English indexes (OR 1.67, 95% CI 0.34-8.30) but was significant in studies identified by searching the Chinese indexes (OR 2.25, 95% CI 1.06-4.77). Egger's test suggested that, for the risk factor of preterm birth, some small studies with negative results might have been missed by the search using the English indexes (Egger's test: P = 0.00).
Conclusions: Searching Chinese literature using English indexes has the potential to fail to identify a substantial number of publications. This bias can result in significant discrepancies in the pooled estimates of risk factors for CP.
Keywords: Cerebral palsy; Chinese; Literature searching; Meta-analysis; Risk factor; Systematic review.
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