13.4 Testing and probing moderation of mediation
13.4.1 A test of moderation of the relative indirect effect.
To get the slopes of Protest vs. No Protest
and Collective vs. Individual Protest
(i.e., \(a_{4}b\) and \(a_{5}b\), respectively), we just work directly with the posterior_samples()
, which we’ve saved as post
.
post <-
post %>%
mutate(a4b = `b_respappr_D1:sexism`*b_liking_respappr,
a5b = `b_respappr_D2:sexism`*b_liking_respappr)
post %>%
select(a4b:a5b) %>%
gather() %>%
group_by(key) %>%
summarize(mean = mean(value),
ll = quantile(value, probs = .025),
ul = quantile(value, probs = .975)) %>%
mutate_if(is.double, round, digits = 3)
## # A tibble: 2 x 4
## key mean ll ul
## <chr> <dbl> <dbl> <dbl>
## 1 a4b 0.307 0.099 0.56
## 2 a5b -0.089 -0.326 0.14
Here they are in a geom_halfeyeh()
plot.
post %>%
select(a4b:a5b) %>%
gather() %>%
ggplot(aes(x = value, y = key)) +
geom_halfeyeh(point_interval = median_qi, .prob = c(0.95, 0.5),
fill = "grey50", color = "white") +
scale_y_discrete(expand = c(.1, .1)) +
labs(x = NULL, y = NULL) +
theme_black() +
theme(axis.ticks.y = element_blank(),
panel.grid.minor.y = element_blank(),
panel.grid.major.y = element_blank())
13.4.2 Probing moderation of mediation.
We already computed the relevant 95% credible intervals at the end of section 13.3 Relative conditional indirect effects. We could inspect those in a geom_halfeyeh()
plot, too.
rcie_tibble_pick_a_point %>%
ggplot(aes(x = value, y = sexism)) +
geom_halfeyeh(point_interval = median_qi, .prob = c(0.95, 0.5),
fill = "grey50", color = "white") +
labs(x = "Relative Conditional Effect on Liking", y = NULL) +
theme_black() +
theme(axis.text.y = element_text(hjust = 0),
panel.grid.minor.y = element_blank(),
panel.grid.major.y = element_blank()) +
facet_wrap(~`indirect effect`)