There are debates in acupuncture-related systematic reviews and meta-analyses on whether searching Chinese databases to get more Chinese-language studies may increase the risk of bias and overestimate the effect size, and whether the treatment effects of acupuncture differ between Chinese and non-Chinese populations.
For this meta-epidemiological study, a team of investigators searched the Cochrane Library from its inception until December 2021, and identified systematic reviews and meta-analyses with acupuncture as one of the interventions. Paired reviewers independently screened the reviews and extracted the information. They repeated the meta-analysis of the selected outcomes to separately pool the results of Chinese- and non-Chinese-language acupuncture studies and presented the pooled estimates as odds ratios (OR) with 95% confidence interval (CI). They calculated the Ratio of ORs (ROR) by dividing the OR of the Chinese-language trials by the OR of the non-Chinese-language trials, and the ROR by dividing the OR of trials addressing Chinese population by the OR of trials addressing non-Chinese population. The researchers thus explored whether the impact of a high risk of bias on the effect size differed between studies published in Chinese- and in non-Chinese-language, and whether the treatment effects of acupuncture differed between Chinese and non-Chinese populations.
The researchers identified 84 Cochrane acupuncture reviews involving 33 Cochrane groups, of which 31 reviews (37%) searched Chinese databases. Searching versus not searching Chinese databases significantly increased the contribution of Chinese-language literature both to the total number of included trials (54% vs. 15%) and the sample size (40% vs. 15%). When compared with non-Chinese-language trials, Chinese-language trials were associated with a larger effect size (pooled ROR 0.51, 95% CI 0.29 to 0.91). The researchers also observed a higher risk of bias in Chinese-language trials in blinding of participants and personnel (97% vs. 51%) and blinding of outcome assessment (93% vs. 47%). The higher risk of bias was associated with a larger effect estimate in both Chinese language (allocation concealment: high/unclear risk vs. low risk, ROR 0.43, 95% CI 0.21 to 0.87) and non-Chinese-language studies (blinding of participants and personnel: high/unclear risk vs. low risk, ROR 0.41, 95% CI 0.23 to 0.74). However, the team found no evidence that the higher risk of bias would increase the effect size of acupuncture in Chinese-language studies more often than in non-Chinese-language studies (the confidence intervals of all ROR in the high-risk group included 1, Table 3). The researchers further found acupuncture appeared to be more effective in Chinese than in non-Chinese populations.
The authors concluded that the findings of this study suggest the higher risk of bias may lead to an overestimation of the treatment effects of acupuncture but would not increase the treatment effects in Chinese-language studies more often than in other language studies. The difference in treatment effects of acupuncture was probably associated with differences in population characteristics.
The authors discuss that, although searching Chinese databases can substantially increase the number of eligible studies and sample size in acupuncture reviews, the potentially higher risk of bias is an argument that needs to be considered in the inclusion of Chinese-language studies. Patients, investigators, and guideline panels should be cautious when adopting evidence from acupuncture reviews where studies with a high risk of bias contributed with a high weight to the meta-analysis.
The authors observed larger treatment effects of acupuncture in Chinese-language studies than in studies published in other languages. Although the treatment effects of acupuncture tended to be greater in studies with a high risk of bias, this potential overestimation did not differ between studies published in Chinese and in other languages. In other words, the larger treatment effects in Chinese-language studies cannot be explained by a high risk of bias. Furthermore, our study found acupuncture to be more effective in Chinese populations than in other populations, which could at least partly explain the larger treatment effects observed in Chinese-language studies.
I feel that this analysis obfuscates more than it clarifies. As we have discussed often here, acupuncture studies by Chinese researchers (regardless of what language they are published in) hardly ever report negative results, and their findings are often fabricated. It, therefore, is not surprising that their effect sizes are larger than those of other trials.
The only sensible conclusion from this messy and regrettable situation, in my view, is to be very cautious and exclude them from systematic reviews.