Before submission of my meta-analysis I want to make a funnel plot to test for heterogeneity and publication bias. I have the pooled effect size and the effect sizes from each study, that take values from -1 to +1. I have the sample sizes n1, n2 for patients and controls from each study. As I cannot calculate the standard error (SE), I cannot perform Egger's regression. I cannot use SE or precision=1/SE on the vertical axis.
- Can I still make a funnel plot with effect size on the horizontal axon and total sample size n (n=n1+n2) on the vertical axis?
- How should such a funnel plot be interpreted?
Some published papers presented such funnel plot with total sample size on the vertical axis (Pubmed PMIDs: 10990474, 10456970). Also, wikipedia funnel plot wiki agree on this. But, most importantly, Mathhias Egger's paper on BMJ 1999 (PubMed PMID: 9451274) shows such a funnel plot, with no SE but only sample size on the vertical axis.
- Is such a plot acceptable when the standard error is not known?
- Is it the same as the classical funnel plot with SE or presicion=1/SE on the vertical axon?
- Is its interpretation different?
- How should I set the lines to make the equilateral triangle?