es_from_md_pval function

Convert a mean difference between two independent groups and its p-value into several effect size measures

es_from_md_pval(
  md,
  md_pval,
  n_exp,
  n_nexp,
  smd_to_cor = "viechtbauer",
  reverse_md
)

Arguments

• md: mean difference between two independent groups
• md_pval: p-value of the mean difference
• n_exp: number of participants in the experimental/exposed group.
• n_nexp: number of participants in the non-experimental/non-exposed group.
• smd_to_cor: formula used to convert the cohen_d value into a coefficient correlation (see details).
• reverse_md: a logical value indicating whether the direction of generated effect sizes should be flipped.

Returns

This function estimates and converts between several effect size measures.

natural effect size measure	MD + D + G
converted effect size measure	OR + R + Z
required input data	See 'Section 10. Mean difference and dispersion (crude)'
	https://metaconvert.org/input.html

Details

This function converts the p-value of a mean difference into a standard error (Cochrane Handbook section 6.5.2.3):

$$t = qt(\frac{md\_pval}{2}, df = n\_exp + n\_nexp - 2)$$ $$md\_se = |\frac{md}{t}|$$

Calculations of the es_from_md_se function are then used to estimate the Cohen's d and other effect size measures.

Examples

es_from_md_pval(md = 4, md_pval = 0.024, n_exp = 20, n_nexp = 22)

References

Higgins JPT, Thomas J, Chandler J, Cumpston M, Li T, Page MJ, Welch VA (editors). Cochrane Handbook for Systematic Reviews of Interventions version 6.3 (updated February 2022). Cochrane, 2022. Available from www.training.cochrane.org/handbook.