walkthrough_blocking: Walkthrough blocking on a covariate

In janhove/cannonball: Tools for Teaching Statistics

Walkthrough blocking on a covariate

Description

This function produces a step-by-step demonstration of how researchers can 'block' on a continuous covariate and how they can analyse the data of a randomised block design.

Usage

walkthrough_blocking(
  n = 10,
  diff = 0,
  sd = 1,
  rho = 0.8,
  showdata = FALSE,
  pedant = FALSE
)

Arguments

n	The number of data points per group.
diff	The boost that participants in the intervention group receive.
sd	The standard deviation of the normal distributions from which the data are drawn.
rho	The correlation between the covariate and the outcome (pre-intervention) in the population.
showdata	Do you want to output a dataframe containing the plotted data (TRUE) or not (FALSE, default)?
pedant	Do you want to run the significance test in pedant mode (TRUE) or not (FALSE, default)? See Details.

Details

Data are generated from a normal distribution with the requested standard deviation; a covariate is also generated. The data points are then grouped in pairs based on their covariate scores. Within each pair, the data points are then randomly assigned to the control or intervention group. Data points in the intervention group receive a boost as specified by 'diff'. Finally, a significance test is ran on the data.

By default, the significance test is a two-sample Student's t-test. Technically, the p-value from this test is the probability that a t-statistic larger than the one observed would've been observed if only chance were at play, but the walkthrough text says that is the probability that a mean difference larger than the one observed would've been observed if only chance were at play. That is, I use the t-test as an approximation to a permutation test. Switch on pedant mode if you want to run a permutation test.

Examples

## Not run: 
walkthrough_blocking(n = 12, diff = 0.2, sd = 1.3, rho = 0.8, pedant = FALSE)

# Save data and double check results
dat <- walkthrough_blocking(n = 12, diff = 0.2, sd = 1.3, rho = 0.8, showdata = TRUE)
anova(lm(score ~ factor(block) + group, data = dat))

# Run in pedant mode (= permutation test)
walkthrough_blocking(n = 12, diff = 0.2, sd = 1.3, rho = 0.8, pedant = TRUE)

## End(Not run)

janhove/cannonball documentation built on Feb. 19, 2025, 5:13 a.m.