A Bland-Altman plot (also known as a difference plot or Tukey mean-difference plot) visualizes the agreement between two measurement methods by plotting the difference against the average of paired observations. It displays the mean difference (bias) as a horizontal line and limits of agreement (mean ± 1.96 SD) to assess whether the methods are interchangeable within acceptable tolerances.
#' anyplot.ai
#' bland-altman-basic: Bland-Altman Agreement Plot
#' Library: ggplot2 3.5.1 | R 4.4.1
#' Quality: 88/100 | Created: 2026-08-11
library(ggplot2)
library(tibble)
library(ragg)
library(scales)
set.seed(42)
# --- Theme tokens -----------------------------------------------------------
THEME <- Sys.getenv("ANYPLOT_THEME", "light")
PAGE_BG <- if (THEME == "light") "#FAF8F1" else "#1A1A17"
ELEVATED_BG <- if (THEME == "light") "#FFFDF6" else "#242420"
INK <- if (THEME == "light") "#1A1A17" else "#F0EFE8"
INK_SOFT <- if (THEME == "light") "#4A4A44" else "#B8B7B0"
INK_MUTED <- if (THEME == "light") "#6B6A63" else "#A8A79F"
IMPRINT_PALETTE <- c(
"#009E73", "#C475FD", "#4467A3", "#BD8233",
"#AE3030", "#2ABCCD", "#954477", "#99B314"
)
# --- Data ---------------------------------------------------------------
# Systolic blood pressure (mmHg) from two sphygmomanometers on 90 subjects
n <- 90
true_sbp <- rnorm(n, mean = 128, sd = 15)
device_a <- true_sbp + rnorm(n, mean = 0, sd = 4)
device_b <- true_sbp + rnorm(n, mean = 2.5, sd = 5)
avg_sbp <- (device_a + device_b) / 2
diff_sbp <- device_a - device_b
bias <- mean(diff_sbp)
sd_diff <- sd(diff_sbp)
loa_upper <- bias + 1.96 * sd_diff
loa_lower <- bias - 1.96 * sd_diff
df <- tibble(avg_sbp = avg_sbp, diff_sbp = diff_sbp)
loa_band <- tibble(x = range(avg_sbp))
annotation_x <- max(avg_sbp) - 0.02 * diff(range(avg_sbp))
# --- Plot -----------------------------------------------------------------
p <- ggplot(df, aes(x = avg_sbp, y = diff_sbp)) +
geom_ribbon(
data = loa_band, aes(x = x, ymin = loa_lower, ymax = loa_upper),
inherit.aes = FALSE, fill = IMPRINT_PALETTE[5], alpha = 0.08
) +
geom_hline(yintercept = 0, color = INK_MUTED, linewidth = 0.4, linetype = "solid") +
geom_hline(yintercept = bias, color = IMPRINT_PALETTE[3], linewidth = 1.1) +
geom_hline(yintercept = loa_upper, color = IMPRINT_PALETTE[5], linewidth = 0.9, linetype = "dashed") +
geom_hline(yintercept = loa_lower, color = IMPRINT_PALETTE[5], linewidth = 0.9, linetype = "dashed") +
geom_point(color = IMPRINT_PALETTE[1], size = 2.5, alpha = 0.6) +
annotate(
"text", x = annotation_x, y = bias, hjust = 1, vjust = -0.6,
label = sprintf("Bias = %.1f mmHg", bias),
size = 4, color = IMPRINT_PALETTE[3]
) +
annotate(
"text", x = annotation_x, y = loa_upper, hjust = 1, vjust = -0.6,
label = sprintf("+1.96 SD = %.1f", loa_upper),
size = 4, color = IMPRINT_PALETTE[5]
) +
annotate(
"text", x = annotation_x, y = loa_lower, hjust = 1, vjust = 1.4,
label = sprintf("-1.96 SD = %.1f", loa_lower),
size = 4, color = IMPRINT_PALETTE[5]
) +
labs(
title = "bland-altman-basic · r · ggplot2 · anyplot.ai",
x = "Mean of Device A and Device B (mmHg)",
y = "Difference: Device A − Device B (mmHg)"
) +
theme_minimal(base_size = 8) +
theme(
plot.background = element_rect(fill = PAGE_BG, color = PAGE_BG),
panel.background = element_rect(fill = PAGE_BG, color = NA),
panel.grid.major = element_line(color = alpha(INK, 0.15), linewidth = 0.4),
panel.grid.minor = element_blank(),
axis.line = element_line(color = INK_SOFT, linewidth = 0.4),
axis.ticks = element_blank(),
axis.title = element_text(color = INK, size = 10),
axis.text = element_text(color = INK_SOFT, size = 8),
plot.title = element_text(color = INK, size = 12, face = "bold"),
plot.margin = margin(t = 14, r = 24, b = 10, l = 10)
)
# --- Save -------------------------------------------------------------------
ggsave(
filename = sprintf("plot-%s.png", THEME),
plot = p,
device = ragg::agg_png,
width = 8,
height = 4.5,
units = "in",
dpi = 400
)
Part of Bland-Altman Agreement Plot on anyplot.ai.