Add a gg funnel function

[Lingtax]

This has some existing implementations (e.g. ce-funnel).

John also has a blog post on this: https://sakaluk.wordpress.com/2016/02/16/7-make-it-pretty-plots-for-meta-analysis/

I suggest it should have options including:

• Contour-enhanced funnel, line at 0, shaded regions for (p<0.1 & p > 0.05) & (p < 0.05 & p > 0.01)
• Standard funnel, line on summary effect size

Point shape by grouping variable may be useful.

[ekothe]

@Lingtax might be work looking at @jsakaluk's repo on contour enhancing funnel plots https://github.com/jsakaluk/ce-funnel

[Lingtax]

Yep, that's why there's a link to that at the very top of this issue @ekothe 😛

[Lingtax]

Wolfgang also has an implementation here: https://github.com/wviechtb/metaggplots/