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## Lollipop Plot: Meta-analysis of Gender Differences in Sexual Behaviour

When I went to the APS conference in San Francisco last year, I got to hear Janet Hyde talk about the gender similarities hypothesis. Broadly, she argues that most gender differences (i.e., men vs. women) in psychological variables tend to be small in size. She used meta-analysis — statistically summarizing the results of lots of published research — as a method of testing her hypothesis. I thought it was fascinating stuff and a great talk, so I wanted to incorporate some of her research into intro psychology. Since I’ve been sprucing up the intro psych section on sex and gender, I thought it would be interesting to include Petersen and Hyde’s (2010) meta-analysis on gender differences in sexual attitudes and behaviour. Broadly, it found that there are a few large sex differences (e.g., men watch more pornography and masturbate more than women), but consistent with her general argument, most differences were very small in size (i.e., smaller than d = .20) and men and women are more similar than different. However, the paper itself doesn’t present the results in a very PowerPoint friendly way, and certainly not intelligible to freshmen students:

So, with that in mind I decided to make a plot up to better visualize the data. The degree of uncertainty displayed by the 95% CI is important … but most in the class don’t actually have any statistics background. So I decided to teach them what “cohen’s d” was first, then create a graph that showed off those numbers. I also taught them that values less than .20 are essentially negligible, so I wanted to highlight that on the plot. I decided on a lollipop plot, which is a bit more appealing than a bar plot.

```library(ggplot2)
library(ggthemes)
library(ggExtra)

#Order the variables in Rank Order

mydata\$name <- factor(mydata\$name, levels = mydata\$name[order(mydata\$d)])

#Create the Plot

ggplot(mydata, aes(x=name, y=d, label=d)) +
geom_point(stat='identity', fill="black", size=6)  +
geom_segment(aes(y = 0,
x = name,
yend = d,
xend = name),
color = "black") +
geom_text(color="white", size=2) +
labs(title="Gender Differences in Sexual Behaviour",
subtitle = "Negative numbers = more common in women; positive numbers = more common in men",
x = "", y = "cohen's d (effect size)") +
ylim(-1, 1) +
theme_bw() +
geom_hline(yintercept = 0, linetype = "solid", color = "grey") +
geom_hline(yintercept = -.20, linetype = "dashed", color = "grey") +
geom_hline(yintercept = .20, linetype = "dashed", color = "grey") +
coord_flip()
```