Add Error Bars to a Plot — error

Adds error bars to an existing plot.

error_bars(
  pos,
  limits = NULL,
  lb = NULL,
  ub = NULL,
  arrow = TRUE,
  flip = FALSE,
  length = 0.05,
  code = 3,
  angle = 90,
  border = NULL,
  ...
)

Arguments

pos: Either a single value or a numeric vector of N values indicating the position(s) at which an error bar should be drawn.
limits: Either a vector of 2 values or a 2 x N matrix giving the lower and upper limits, respectively, of the error bars.
lb: A vector of N values with the lower limits for the error bars.
ub: A vector of N values with the upper limits for the error bars.
arrow: Logical; if TRUE, arrows are drawn at each position, otherwise a call is made to polygon to create a filled-in segment to represent connected error bars.
flip: Logical; if TRUE, bars are drawn horizontally instead of vertically. In this case pos denotes the position(s) on the y-axis. Otherwise, pos denotes the position(s) on the x-axis.
length: The length of the arrowhead for the call to arrows.
code: Integer controlling whether to draw an arrowhead at the start (1), end (2), or at both ends (3) of the line for the call to arrows.
angle: The angle of the lines creating the arrowhead for the call to arrows. Using 90 degrees results in a flat bar per standard error bars.
border: The color to draw the border for polygon.
...: Additional plotting parameters for the arrows function, or if arrow is FALSE, polygon.

Examples

# Simulate 5 variables with increasing means
dtf <- lapply(lin(-.5, .5, 5), function(x) rnorm(100, mean = x))
names(dtf) <- paste0("V", 1:5)
dtf <- data.frame(dtf)
# Extract sample means and standard errors
sm <- data.frame(
  M = colMeans(dtf),
  SE = apply(dtf, 2, sem)
)
# Compute 95% confidence intervals around
# sample means
sm$LB <- sm$M + qnorm(.025) * sm$SE
sm$UB <- sm$M + qnorm(.975) * sm$SE

# Plot mean for each variable
plot(1:5, sm$M,
  pch = 19,
  xlab = "Variable", ylab = "Mean", ylim = c(-1, 1)
)
# Add error bars (as arrows) for 95% confidence intervals
error_bars(1:5, rbind(sm$LB, sm$UB))
# Add error bars (as connected filled segment)
error_bars(1:5, rbind(sm$LB, sm$UB),
 arrow = FALSE, col = rgb(.5, .5, .5, .2), border = NA
)


# Histogram for draws from standard normal
set.seed(300)
x <- rnorm(1000)
hist(x,
  col = "grey", border = "white", main = "",
  xlab = "z-scores", freq = FALSE, xlim = c(-4, 4)
)
# Add horizontal bars showing difference between
# 95% and 68% coverage interval
error_bars(c(.1, .3),
  lb = qnorm(c(.025, .16)), ub = qnorm(c(.975, .84)),
  lwd = 2, flip = TRUE
)
# Label bars
text(c(-2.1, -1.1), c(.1, .3),
  c("95%", "68%"),
  pos = 2
)