An Evaluation of Alternative Methods for Computing Standardized Mean Difference Effect Size

Background Most meta-analyses use the ‘standardised mean difference’ (effect size) to summarise the outcomes of studies. However, the effect size has important limitations that need to be considered. Method After a brief explanation of the standardized mean difference, limitations are discussed and possible solutions in the context of meta-analyses are suggested. Results When using the effect size, three major limitations have to be considered. First, the effect size is still a statistical concept and small effect sizes may have considerable clinical meaning while large effect sizes may not. Second, specific assumptions of the effect size may not be correct. Third, and most importantly, it is very difficult to explain what the meaning of the effect size is to non-researchers. As possible solutions, the use of the ‘binomial effect size display’ and the number-needed-to-treat are discussed. Furthermore, I suggest the use of binary outcomes, which are often easier to understand. However, it is not clear what the best binary outcome is for continuous outcomes. Conclusion The effect size is still useful, as long as the limitations are understood and also binary outcomes are given.

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Between‐case standardized mean difference effect sizes for single‐case designs: a primer and tutorial using the scdhlm web application

Campbell Systematic Reviews ◽

10.4073/cmdp.2016.1 ◽

2016 ◽

Vol 12 (1) ◽

pp. 1-31 ◽

Cited By ~ 16

Author(s):

Jeffrey C. Valentine ◽

Emily E. Tanner‐Smith ◽

James E. Pustejovsky ◽

T. S. Lau

Keyword(s):

Web Application ◽

Single Case ◽

Mean Difference ◽

Effect Sizes ◽

Standardized Mean Difference ◽

Single Case Designs ◽

Difference Effect

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Statistical Inference in Adaptive Group Sequential Trials with the Standardized Mean Difference as Effect Size

Sequential Analysis ◽

10.1080/07474946.2011.539926 ◽

2011 ◽

Vol 30 (1) ◽

pp. 94-113 ◽

Cited By ~ 2

Author(s):

Joachim Hartung ◽

Guido Knapp

Keyword(s):

Statistical Inference ◽

Effect Size ◽

Mean Difference ◽

Group Sequential ◽

Group Sequential Trials ◽

Standardized Mean Difference ◽

Sequential Trials

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Comparing Short Dental Implants to Standard Dental Implants: Protocol for a Systematic Review (Preprint)

10.2196/preprints.8836 ◽

2017 ◽

Author(s):

Amir Reza Rokn ◽

Abbasali Keshtkar ◽

Abbas Monzavi ◽

Kazem Hashemi ◽

Tahereh Bitaraf

Keyword(s):

Systematic Review ◽

Survival Rate ◽

Confidence Interval ◽

Dental Implants ◽

Effect Size ◽

Group Analysis ◽

Mean Difference ◽

Controlled Trials ◽

Cochrane Central Register ◽

Standardized Mean Difference

BACKGROUND Short dental implants have been proposed as a simpler, cheaper, and faster alternative for the rehabilitation of atrophic edentulous areas to avoid the disadvantages of surgical techniques for increasing bone volume. OBJECTIVE This review will compare short implants (4 to 8 mm) to standard implants (larger than 8 mm) in edentulous jaws, evaluating on the basis of marginal bone loss (MBL), survival rate, complications, and prosthesis failure. METHODS We will electronically search for randomized controlled trials comparing short dental implants to standard dental implants in the following databases: PubMed, Web of Science, EMBASE, Scopus, the Cochrane Central Register of Controlled Trials, and ClinicalTrials.gov with English language restrictions. We will manually search the reference lists of relevant reviews and the included articles in this review. The following journals will also be searched: European Journal of Oral Implantology, Clinical Oral Implants Research, and Clinical Implant Dentistry and Related Research. Two reviewers will independently perform the study selection, data extraction and quality assessment (using the Cochrane Collaboration tool) of included studies. All meta-analysis procedures including appropriate effect size combination, sub-group analysis, meta-regression, assessing publication or reporting bias will be performed using Stata (Statacorp, TEXAS) version 12.1. RESULTS Short implant effectiveness will be assessed using the mean difference of MBL in terms of weighted mean difference (WMD) and standardized mean difference (SMD) using Cohen’s method. The combined effect size measures in addition to the related 95% confidence intervals will be estimated by a fixed effect model. The heterogeneity of the related effect size will be assessed using a Q Cochrane test and I2 measure. The MBL will be presented by a standardized mean difference with a 95% confidence interval. The survival rate of implants, prostheses failures, and complications will be reported using a risk ratio at 95% confidence interval (P<.05). CONCLUSIONS The present protocol illustrates an appropriate method to perform the systematic review and ensures transparency for the completed review. The results will be published in a peer-reviewed journal and social networks. In addition, an ethics approval is not considered necessary. CLINICALTRIAL PROSPERO registration number: CRD42016048363; https://www.crd.york.ac.uk/PROSPERO/ display_record.asp?ID=CRD42016048363 (Archived by WebCite at http://www.webcitation.org/6wZ7Fntry)

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