One Sample T-Test

The Student’s One-sample t-test is used to test the null hypothesis that the true mean is equal to a particular value (typically zero). A low p-value suggests that the null hypothesis is not true, and therefore the true mean must be different from the test value.

The Student’s One-sample t-test assumes that the data are from a normal distribution – in the case that one is unwilling to assume this, the non-parametric Wilcoxon signed-rank can be used in it’s place (However, note that the Wilcoxon signed-rank has a slightly different null hypothesis; that the median is equal to the test value).

Example usage


ttestOneS(ToothGrowth, vars = vars(len, dose))

#  One Sample T-Test
#  ──────────────────────────────────────────────────────
#                           statistic    df      p
#  ──────────────────────────────────────────────────────
#    len     Student's t         19.1    59.0    < .001
#    dose    Student's t         14.4    59.0    < .001
#  ──────────────────────────────────────────────────────


data the data as a data frame
vars a vector of strings naming the variables of interest in data
students TRUE (default) or FALSE, perform Student's t-tests
bf TRUE or FALSE (default), provide Bayes factors
bfPrior a number between 0.5 and 2.0 (default 0.707), the prior width to use in calculating Bayes factors
wilcoxon TRUE or FALSE (default), perform Wilcoxon signed rank tests
testValue a number specifying the value of the null hypothesis
hypothesis 'dt' (default), 'gt' or 'lt', the alternative hypothesis; different to testValue, greater than testValue, and less than testValue respectively
norm TRUE or FALSE (default), perform Shapiro-wilk tests of normality
qq TRUE or FALSE (default), provide a Q-Q plot of residuals
meanDiff TRUE or FALSE (default), provide means and standard deviations
effectSize TRUE or FALSE (default), provide Cohen's d effect sizes
ci TRUE or FALSE (default), provide confidence intervals for the mean difference
ciWidth a number between 50 and 99.9 (default: 95), the width of confidence intervals
desc TRUE or FALSE (default), provide descriptive statistics
plots TRUE or FALSE (default), provide descriptive plots
miss 'perAnalysis' or 'listwise', how to handle missing values; 'perAnalysis' excludes missing values for individual dependent variables, 'listwise' excludes a row from all analyses if one of its entries is missing.


A results object containing:

results$ttest a table
results$normality a table
results$descriptives a table
results$plots an image
results$qq an array of images

Tables can be converted to data frames with asDF or For example:


Elements in arrays can be accessed with [[n]]. For example:

results$qq[[1]] # accesses the first element