Tests of Uniformity and Independence for Terminal Digits.
terminaldigits
The package terminaldigits implements simulated tests of uniformity and independence for terminal digits. For certain parameters, terminaldigits also implements Monte Carlo simulations for type I errors and power for the test of independence. Simulations are run in C++ utilizing Rcpp.
Installation
You can install the development version of terminaldigits from GitHub with:
# install.packages("devtools")
devtools::install_github("josh-mc/terminaldigits")
Usage
In many cases, terminal digits can be assumed to be uniformly distributed and independent of preceding digits. A violation of either of these assumptions may point to a data quality issue.
The following examples are based on a data set taken from the third round of a decoy experiment involving hand-washing purportedly carried out in a number of factories in China. For details, see decoy and Yu, Nelson, and Simonsohn (2018).
The td_uniformity function tests the assumption of uniformity using Pearson’s chi-squared statistic for goodness-of-fit.
library(terminaldigits)
td_uniformity(decoy$weight, decimals = 2, reps = 1000)
#>
#> Pearson's chi-squared GOF test for uniformity of terminal digits
#>
#> data: decoy$weight
#> Chi-squared = 539.67, p-value = 0.000999
The td_independence function tests the assumption of independence. The default statistic is again Pearson’s chi-squared statistic but the log-likelihood ratio statistic, the Freeman-Tukey statistic, and the root-mean-square statistic are also available.
td_independence(decoy$weight, decimals = 2, reps = 1000)
#>
#> Chisq test for independence of terminal digits
#>
#> data: decoy$weight
#> Chisq = 6422.4, p-value = 0.000999
The td_test function is a wrapper for the above two functions. For more details, including a discussion of the td_simulate function, see the package introduction vignette.
References
Yu, F., Nelson, L., & Simonsohn, U. (2018, December 5). “In Press at Psychological Science: A New ‘Nudge’ Supported by Implausible Data.” DataColoda 74. http://datacolada.org/74