lineup_qq: Check distributional assumptions using Q-Q plots and the...

In nullabor: Tools for Graphical Inference

Check distributional assumptions using Q-Q plots and the lineup protocol.

Description

This function is used to quickly create lineup plots to check distributional assumptions using Q-Q plots. The null hypothesis is that the data follows the distribution specified by the dist argument. In the lineup protocol the plot of the real data is embedded amongst a field of plots of data generated to be consistent with some null hypothesis. If the observer can pick the real data as different from the others, this lends weight to the statistical significance of the structure in the plot. The protocol is described in Buja et al. (2009).

Usage

lineup_qq(
  data,
  variable,
  dist = NULL,
  params = NULL,
  color_points = "black",
  color_lines = "brown3",
  alpha_points = 0.5
)

Arguments

data	a data frame.
variable	the name of the variable that should be plotted.
dist	the null distribution name. One of: "beta", "cauchy", "chi-squared", "exponential", "f", "gamma", "geometric", "log-normal", "lognormal", "logistic", "negative binomial", "normal", "poisson", "t", "uniform", "weibull"
params	list of parameters of distribution. If NULL, will use fitdistr to estimate them if possible. For uniform and beta distributions, the parameters must be specified. See ?dunif and ?dbeta for parameter names.
color_points	the color used for points. Can be a name or a color HEX code.
color_lines	the color used for reference lines.
alpha_points	the alpha (opacity) used for points (between 0 and 1, where 1 is opaque).

Details

19 null datasets are plotted together the the true data (randomly positioned) If you pick the real data as being noticeably different, then you have formally established that it is different to with p-value 0.05.

Run the decrypt message printed in the R Console to see which plot represents the true data.

Value

a ggplot

References

Buja, Cook, Hofmann, Lawrence, Lee, Swayne, Wickham. (2009). Statistical inference for exploratory data analysis and model diagnostics, Phil. Trans. R. Soc. A, 367, 4361-4383.

See Also

null_dist

Examples

data(tips)
lineup_qq(tips, "total_bill", dist = "normal") # Normal distribution
lineup_qq(tips, "total_bill", dist = "gamma") # Gamma distribution

# Some distributions require that the parameters be specified:
tips$proportion_tips <- tips$tip/(tips$total_bill+tips$tip)
lineup_qq(tips, "size", dist = "beta", params = list(shape1 = 0.1, shape2 = 0.2))

# Style the plot using color settings and ggplot2 functions:
lineup_qq(tips, "total_bill",
          dist = "gamma",
          color_points = "chocolate",
          color_lines = "cyan",
          alpha_points = 0.25) +
    ggplot2::theme_minimal()

nullabor documentation built on April 4, 2025, 4:14 a.m.