72 Dumbell Plot

In this chapter, we draw a dumbell plot using ggplot. We do this using the first 10 record of systolic blood pressures measured 6 months apart for a group of hypertensive patients.

Code

df_dbl <- 
    readxl::read_xlsx("C:/Dataset/SBPDATA.xlsx") %>% 
    janitor::clean_names() %>% 
    select(sid, sbp_0, sbp_6) %>% 
    drop_na() %>% 
    mutate(
        sid = paste0("GHA-", sid),
        mean_bp = (sbp_0 + sbp_6)/2,
        diff_sbp = (sbp_6 - sbp_0),
        diff_sbp_cat = case_when(
            diff_sbp < 0 ~ "red", diff_sbp >= 0 ~ "black")) %>% 
    head(n=10)

df_dbl_long <-  
    df_dbl %>% 
    pivot_longer(
        cols = starts_with("sbp"), 
        names_to = "Month", 
        values_to = "SBP")

Next, we visualise the data

Code

df_dbl %>% head() %>% kableExtra::kable()

sid	sbp_0	sbp_6	mean_bp	diff_sbp	diff_sbp_cat
GHA-1	139	130	134.5	-9	red
GHA-3	109	126	117.5	17	black
GHA-5	124	144	134.0	20	black
GHA-6	140	117	128.5	-23	red
GHA-7	137	147	142.0	10	black
GHA-10	135	150	142.5	15	black

Code

df_dbl_long %>% head() %>% kableExtra::kable()

sid	mean_bp	diff_sbp	diff_sbp_cat	Month	SBP
GHA-1	134.5	-9	red	sbp_0	139
GHA-1	134.5	-9	red	sbp_6	130
GHA-3	117.5	17	black	sbp_0	109
GHA-3	117.5	17	black	sbp_6	126
GHA-5	134.0	20	black	sbp_0	124
GHA-5	134.0	20	black	sbp_6	144

Then, we plot the diagram

Code

df_dbl_long %>% 
    ggplot(aes(x = SBP, y = sid, fill = Month))+
    
    labs(y = NULL)+
    geom_segment(
        data = df_dbl, 
        aes(x = sbp_0, xend = sbp_6, y = sid, color = diff_sbp_cat), 
        inherit.aes = F)+
    geom_point(size = 5, color = "black", shape = 21)+
    annotate(
        geom = "text",
        x = df_dbl$mean_bp, 
        y = df_dbl$sid, 
        label = df_dbl$diff_sbp,
        color = df_dbl$diff_sbp_cat,
        size = 3.5, vjust = -0.3)+
    theme_bw()+
    scale_color_discrete(
        breaks = c("sbp_0", "sbp_6"),
        labels = c("Month 0", "Month 6"))+
    scale_fill_manual(
        breaks = c("sbp_0", "sbp_6"),
        labels = c("Month 0", "Month 6"),
        values = c("white", "#75AADB"))+
    scale_color_identity()+
    theme(
        legend.position = "top", 
        legend.title = element_blank(), 
        legend.box.background  = element_rect(color = "black"))

Scale for colour is already present.
Adding another scale for colour, which will replace the existing scale.

Figure 72.1: Dumbell showing change in blood pressure