seq_ttest: Sequential Probability Ratio Test using t-statistic

In sprtt: Sequential Probability Ratio Tests Toolbox

Sequential Probability Ratio Test using t-statistic

Description

Performs one and two sample sequential t-tests on vectors of data. For more information on the sequential t-test, see Schnuerch & Erdfelder (2019) doi:10.1037/met0000234.

Usage

seq_ttest(
  x,
  y = NULL,
  data = NULL,
  mu = 0,
  d,
  alpha = 0.05,
  power = 0.95,
  alternative = "two.sided",
  paired = FALSE,
  na.rm = TRUE,
  verbose = TRUE
)

Arguments

x	Works with two classes: numeric and formula. Therefore you can write "x" or "x~y". "numeric input": a (non-empty) numeric vector of data values. "formula input": a formula of the form lhs ~ rhs where lhs is a numeric variable giving the data values and rhs either 1 for a one-sample test or a factor with two levels giving the corresponding groups.
y	an optional (non-empty) numeric vector of data values.
data	an optional data.frame, which you can use only in combination with a "formula input" in argument x.
mu	a number indicating the true value of the mean (or difference in means if you are performing a two sample test).
d	a number indicating the specified effect size (Cohen's d)
alpha	the type I error. A number between 0 and 1.
power	1 - beta (beta is the type II error probability). A number between 0 and 1.
alternative	a character string specifying the alternative hypothesis, must be one of two.sided (default), greater or less. You can specify just the initial letter.
paired	a logical indicating whether you want a paired t-test.
na.rm	a logical value indicating whether NA values should be stripped before the computation proceeds.
verbose	a logical value whether you want a verbose output or not.

Value

An object of the S4 class seq_ttest_results. Click on the class link to see the full description of the slots. To get access to the object use the @-operator or ⁠[]⁠-brackets instead of $. See the examples below.

Examples

# set seed --------------------------------------------------------------------
set.seed(333)

# load library ----------------------------------------------------------------
library(sprtt)

# one sample: numeric input ---------------------------------------------------
treatment_group <- rnorm(20, mean = 0, sd = 1)
results <- seq_ttest(treatment_group, mu = 1, d = 0.8)

# get access to the slots -----------------------------------------------------
# @ Operator
results@likelihood_ratio

# [] Operator
results["likelihood_ratio"]

# two sample: numeric input----------------------------------------------------
treatment_group <- stats::rnorm(20, mean = 0, sd = 1)
control_group <- stats::rnorm(20, mean = 1, sd = 1)
seq_ttest(treatment_group, control_group, d = 0.8)

# two sample: formula input ---------------------------------------------------
stress_level <- stats::rnorm(20, mean = 0, sd = 1)
sex <- as.factor(c(rep(1, 10), rep(2, 10)))
seq_ttest(stress_level ~ sex, d = 0.8)

# NA in the data --------------------------------------------------------------
stress_level <- c(NA, stats::rnorm(20, mean = 0, sd = 2), NA)
sex <- as.factor(c(rep(1, 11), rep(2, 11)))
seq_ttest(stress_level ~ sex, d = 0.8, na.rm = TRUE)

# work with dataset (data are in the package included) ------------------------
seq_ttest(monthly_income ~ sex, data = df_income, d = 0.8)

sprtt documentation built on July 9, 2023, 6:14 p.m.