Make curves thicker in R quickpsy

I'm using quickpsy package in R (https://cran.r-project.org/web/packages/quickpsy/quickpsy.pdf /
http://dlinares.org/quickpsy.html) to fit psychometric functions to the data. I use quickpsy and then plotcurves.

fit <- quickpsy(data, delta, response, grouping = c("condition"),lapses = FALSE, bootstrap = "none",  fun = logistic_fun) 

plotcurves(fit,  ci = TRUE) + labs(y = "Proportion yes responses", x="Delta") + theme_classic(base_size = 20)  + scale_x_continuous(n.breaks = 6, limits=c(-3, 3)) + 
scale_color_manual(values=c("#C0C0C0", "#000000")) + theme(legend.title = element_blank())

I'd like to make the plotted curves thicker. Is there any way to do it? I couldn't increase the thickness with any ggplot width manipulation.

Solution

What you could do is using your quickpsy fit with ggplot instead of plotcurves. Then you can change the size of your geom_line. Here is a reproducible example:

library(ggplot2)
library(quickpsy)

x <- seq(0, 420, 60)
k <- c(0, 0, 4, 18, 20, 20, 19, 20)
dat <- tibble(x, k, n = 20)

fitWithoutLapses <- quickpsy(dat, x, k, n, prob = .75) 
#> Warning: `group_by_()` was deprecated in dplyr 0.7.0.
#> Please use `group_by()` instead.
#> See vignette('programming') for more help
#> This warning is displayed once every 8 hours.
#> Call `lifecycle::last_lifecycle_warnings()` to see where this warning was generated.

curvesWithoutLapses <- fitWithoutLapses$curves %>% 
  mutate(cond = 'Without Lapses')

pWithout <- ggplot()+
  geom_point(data = fitWithoutLapses$averages, aes(x = x, y = prob)) +
  geom_line(data = curvesWithoutLapses,
            aes(x = x, y = y, color = cond), size = 2) +
  geom_linerange(data = fitWithoutLapses$thresholds, 
                 aes(x = thre, ymin = 0, ymax = prob), lty =2) 
pWithout

^{Created on 2022-07-30 by the reprex package (v2.0.1)}

For more info check this link for using quickpsy in ggplot.