jmv

Independent Samples T-Test

Example usage

data('ToothGrowth')

ttestIS(data = ToothGrowth, vars = 'len', group = 'supp')

#
#  Independent Samples T-Test
#
#  Independent Samples T-Test
#  ────────────────────────────────────────────────────
#                          statistic    df      p
#  ────────────────────────────────────────────────────
#    len    Student's t         1.92    58.0    0.060
#  ────────────────────────────────────────────────────
#

Arguments

data the data as a data frame
vars a vector of strings naming the dependent variables
group a string naming the grouping variable, must have 2 levels
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 (default 0.707), the prior width to use in calculating Bayes factors
welchs TRUE or FALSE (default), perform Welch's t-tests
mann TRUE or FALSE (default), perform Mann-Whitney U tests
hypothesis 'different' (default), 'oneGreater' or 'twoGreater', the alternative hypothesis; group 1 different to group 2, group 1 greater than group 2, and group 2 greater than group 1 respectively
norm TRUE or FALSE (default), perform Shapiro-Wilk test of normality
eqv TRUE or FALSE (default), perform Levene's test for equality of variances
meanDiff TRUE or FALSE (default), provide means and standard errors
effectSize TRUE or FALSE (default), provide effect sizes
ci TRUE or FALSE (default), provide confidence intervals
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.

Returns

A results object containing:

results$ttest a table
results$assum$norm a table
results$assum$eqv a table
results$desc a table
results$plots an array of images

Tables can be converted to data frames with asDF or as.data.frame(). For example:

results$ttest$asDF

as.data.frame(results$ttest)

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

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