Dear Editor,
Tolppola and coworkers published a systematic review and meta-analysis of pacifier usage in term and preterm newborns [1]. The authors chose a meta-analysis model based on I2, which depicts a percentage of total variability due to between-study variability, and it depends on the size of studies.
The authors inconsistently stated that I2 threshold of either 40% or 50% was used for selection of fixed or random-effects model. A crude guide to interpret I2 in the context of randomized trials is provided while recognized that thresholds can be misleading, since several factors exist like confidence interval (CI) for I2 [2].
The choice between models should not be based on I2 or P-value for homogeneity as touched in another comment on the authors’ systematic review [3]. However, selection of fixed or random-effects model based on I2 has shown to be frequent [4].
Two “positive” outcomes were observed based on four studies [1]. I2 was 33% for duration of hospital stay and 42% for time to full oral feeding, thus the authors adopted inverse variance weighted fixed effect model, which assumes one fixed (viz. common) true effect across studies. Nonetheless, 95% CI for I2 would be 0–76% and 0–81%, thus underscoring uncertainty of I2 [5].
I reanalyzed the two outcomes with the recommended random-effects model [6]. Average mean difference between restricted and nonrestricted pacifier use in preterm infants was 7.23 (95% CI 0.77 to 13.68) days for hospital stay and 3.21 (95% CI –1.12 to 7.55) days for time to full oral feeding. As expected, CIs became wider with the random-effects model and the latter CI includes 0 for imprecision.
To conclude, sensitivity analyses within meta-analyses are justified since methods matter [7].
Abbreviations
- CI:
-
Confidence interval
References
Tolppola O, Renko M, Sankilampi U et al (2022) Pacifier use and breastfeeding in term and preterm newborns-a systematic review and meta-analysis. Eur J Pediatr 181:3421–3428. https://doi.org/10.1007/s00431-022-04559-9
Higgins JPT, Thomas J, Chandler J et al (editors) (2022) Cochrane handbook for systematic reviews of interventions version 6.3 (updated Febr 2022). Cochrane. www.training.cochrane.org/handbook (Accessed 23 Aug 2022)
Kumar J, Meeta J (2022) Concerns in a systematic review on pacifier use and breastfeeding in infants. Eur J Pediatr. https://doi.org/10.1007/s00431-022-04589-3
Riley RD, Gates S, Neilson J et al (2011) Statistical methods can be improved within Cochrane pregnancy and childbirth reviews. J Clin Epidemiol 64:608–618. https://doi.org/10.1016/j.jclinepi.2010.08.002
Ioannidis JP, Patsopoulos NA, Evangelou E (2007) Uncertainty in heterogeneity estimates in meta-analyses. BMJ 335:914–916. https://doi.org/10.1136/bmj.39343.408449.80
Langan D, Higgins JPT, Jackson D et al (2019) A comparison of heterogeneity variance estimators in simulated random-effects meta-analyses. Res Synth Methods 10:83–98. https://doi.org/10.1002/jrsm.1316
Kivelä JM (2020) Effects of nutritional supplements and dietary interventions on cardiovascular outcomes. Ann Intern Med 172:73–74. https://doi.org/10.7326/L19-0714
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Communicated by Daniele De Luca
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Kivelä, J.M. Do methods in meta-analyses matter?. Eur J Pediatr 181, 3989 (2022). https://doi.org/10.1007/s00431-022-04618-1
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DOI: https://doi.org/10.1007/s00431-022-04618-1