Author’s reply: Letter to the Editor: Double counting due to inadequate statistics leads to false-positive findings in “Effects of creatine supplementation on memory in healthy individuals: a systematic review and meta-analysis of randomized controlled trials”
Bibliographic record
Abstract
In their Letter to the Editor, Eckert and Pascher1 correctly identified a flawed statistical analysis that warranted correction pertaining to the increased statistical power of our previous meta-analysis on creatine supplementation and memory performance.2 The inclusion of multiple memory-related outcomes from each study was accompanied with an increased number of the same participants (double counting). This could have altered the outcome estimates in the meta-analyses, indeed leading to an increased risk of false-positive findings. To address this, we have now derived the average effect size for studies presenting multiple memory performance outcomes (expressed as a composite score) through pooled means and standard deviations for each intervention group. After correction, our overall analysis showed that creatine monohydrate does not improve overall memory performance (standardized mean difference [SMD], 0.19; 95% confidence interval [CI], –0.07, 0.46; I2 = 4%; P = 0.15) (Figure 1). Subgroup analyses revealed no differences of creatine monohydrate supplementation with low (≤5 g/day; SMD, 0.25; 95%CI, –0.14, 0.64; I2 = 0%; P = 0.21) or high (>5 g/d; SMD, 0.17; 95%CI, –0.34, 0.69; I2 = 50%; P = 0.51) doses (Figure 2A). However, although young adults (aged 11–31 years) did not benefit from creatine monohydrate (SMD, 0.02; 95%CI, –0.27, 0.31; I2 = 0%, P = 0.90), its effects were prominent in older adults (aged 66–76 years; SMD, 0.80; 95%CI, 0.25–1.34; I2 = 0%; P = 0.004) (Figure 2B), which was the main finding of our previous work.2 Furthermore, no changes were displayed regarding treatment duration (≤2 weeks: SMD, 0.16 [95%CI, –0.23, 0.56], I2 = 33%, P = 0.42; >2 weeks: SMD, 0.30 [95%CI, –0.17, 0.76], I2 = 0%, P = 0.21) (Figure 2C) nor sex (women and men: SMD, 0.18 [95%CI, –0.20, 0.56, I2 = 31%, P = 0.36; women: SMD, 0.42 [95%CI, –0.14, 0.98], I2 = 0%, P = 0.14; men: SMD, –0.11 [95%CI, –1.01, 0.79], P = 0.81) (Figure 2D). Our sensitivity analyses showed no effects of creatine monohydrate on memory performance in nonencapsulated form (SMD, 0.22; 95%CI, –0.08, 0.52; I2 = 16%; P = 0.15) (Figure 3A), normal (SMD, 0.29; 95%CI, –0.09, 0.68; I2 = 35%; P = 0.14) or stressed conditions (SMD, 0.03; 95%CI, –0.46, 0.52; I2 = 0%; P = 0.91) (Figure 3B), and participants lost to follow-up (<15%) (SMD, 0.28; 95%CI, –0.02, 0.59; I2 = 1%; P = 0.07) (Figure 3C).
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.020 | 0.139 |
| Meta-epidemiology (narrow) | 0.002 | 0.002 |
| Meta-epidemiology (broad) | 0.004 | 0.004 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.003 | 0.004 |
| Scholarly communication | 0.005 | 0.005 |
| Open science | 0.005 | 0.002 |
| Research integrity | 0.033 | 0.037 |
| Insufficient payload (model declined to judge) | 0.008 | 0.011 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".