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digitTests is an R package providing statistical tests
for detecting irregular digit patterns. Such irregular digit patterns
can be an indication of potential data manipulation or fraud. Therefore,
the type of tests that the package provides can be useful in (but not
limited to) the field of auditing to assess whether data have
potentially been tampered with. However, please note that real data will
never be perfect, and therefore caution should be used when relying on
the statistical decision metrics that the package provides.
The package is also implemented with a graphical user interface in the Audit module of JASP, a free and open-source statistical software program.
For complete documentation of the digitTests package
download the package
manual.
The most recently released version of digitTests can be
downloaded from CRAN by running
the following command in R:
install.packages('digitTests')Alternatively, you can download the development version from GitHub using:
devtools::install_github('koenderks/digitTests')After installation, the package can be loaded with:
library(digitTests)To validate the statistical results, digitTests’s
automated unit
tests regularly verify the main output from the package against the
following benchmarks:
extract_digits()The workhorse of the package is the extract_digits()
function. This function takes a vector of numbers and returns the
requested digits (with or without including 0’s).
Full function with default arguments:
extract_digits(x, check = 'first', include.zero = FALSE)Supported options for the check argument:
check |
Returns |
|---|---|
fist |
First digit |
firsttwo |
First and second digit |
before |
All digits before the decimal separator
(.) |
after |
All digits after the decimal separator
(.) |
lasttwo |
Last two digits |
last |
Last digit |
Example:
x <- c(0.00, 0.20, 1.23, 40.00, 54.04)
extract_digits(x, check = 'first', include.zero = FALSE)
# [1] NA 2 1 4 5distr.test() & distr.btest()The functions distr.test() and
distr.btest() take a vector of numeric values, extract the
requested digits, and compares the frequencies of these digits to a
reference distribution. The function distr.test() performs
a frequentist hypothesis test of the null hypothesis that the digits are
distributed according to the reference distribution and produces a
p value. The function distr.btest() performs a
Bayesian hypothesis test of the null hypothesis that the digits are
distributed according to the reference distribution against the
alternative hypothesis (using the prior parameters specified in
alpha) that the digits are not distributed according to the
reference distribution and produces a Bayes factor (Kass & Raftery,
1995). The possible options for the check argument are
taken over from extract_digits().
Full function with default arguments:
distr.test(x, check = 'first', reference = 'benford')
distr.btest(x, check = 'first', reference = 'benford', alpha = NULL, BF10 = TRUE, log = FALSE)Supported options for the reference
argument:
check |
Returns |
|---|---|
benford |
Benford’s law |
uniform |
Uniform distribution |
| Vector of probabilities | Custom distribution |
Example:
Benford’s law (Benford, 1938) is a principle that describes a pattern in many naturally-occurring numbers. According to Benford’s law, each possible leading digit d in a naturally occurring, or non-manipulated, set of numbers occurs with a probability:
The distribution of leading digits in a data set of financial
transaction values (e.g., the sinoForest data) can be
extracted and tested against the expected frequencies under Benford’s
law using the code below.
# Frequentist hypothesis test
distr.test(sinoForest$value, check = 'first', reference = 'benford')
#
# Digit distribution test
#
# data: sinoForest$value
# n = 772, X-squared = 7.6517, df = 8, p-value = 0.4682
# alternative hypothesis: leading digit(s) are not distributed according to the benford distribution.
# Bayesian hypothesis test using default prior
distr.btest(sinoForest$value, check = 'first', reference = 'benford', BF10 = FALSE)
#
# Digit distribution test
#
# data: sinoForest$value
# n = 772, BF01 = 6899678
# alternative hypothesis: leading digit(s) are not distributed according to the benford distribution.rv.test()The function rv.test() analyzes the frequency with which
values get repeated within a set of numbers. Unlike Benford’s law, and
its generalizations, this approach examines the entire number at once,
not only the first or last digit. For the technical details of this
procedure, see Simohnsohn (2019). The possible options for the
check argument are taken over from
extract_digits().
Full function with default arguments:
rv.test(x, check = 'last', method = 'af', B = 2000)Supported options for the method argument:
check |
Returns |
|---|---|
af |
Average frequency |
entropy |
Entropy |
Example:
In this example we analyze a data set from a (retracted) paper that
describes three experiments run in Chinese factories, where workers were
nudged to use more hand-sanitizer. These data were shown to exhibited
two classic markers of data tampering: impossibly similar means and the
uneven distribution of last digits (Yu, Nelson, & Simohnson, 2018).
We can use the rv.test() function to test if these data
also contain a greater amount of repeated values than expected if the
data were not tampered with.
rv.test(sanitizer$value, check = 'lasttwo', B = 5000)
#
# Repeated values test
#
# data: sanitizer$value
# n = 1600, AF = 1.5225, p-value = 0.0024
# alternative hypothesis: frequencies of repeated values are greater than for random data.These binaries (installable software) and packages are in development.
They may not be fully stable and should be used with caution. We make no claims about them.