tab (version 2.1.1)

tabmeans: Generate summary tables of mean comparisons for statistical reports

Description

This function compares the mean of a continuous variable across levels of a factor variable and summarizes the results in a clean table for a statistical report.

Usage

tabmeans(x, y, latex = FALSE, xlevels = NULL, yname = "Y variable", decimals = 1, 
         p.decimals = c(2, 3), p.cuts = 0.01, p.lowerbound = 0.001, p.leading0 = TRUE, 
         p.avoid1 = FALSE, n = FALSE, se = FALSE)

Arguments

x

Vector of values for the factor variable.

y

Vector of values for the continuous variable.

latex

If TRUE, object returned will be formatted for printing in LaTeX using xtable [1]; if FALSE, it will be formatted for copy-and-pasting from RStudio into a word processor.

xlevels

Optional character vector to label the levels of x. If unspecified, the function uses generic labels.

yname

Optional label for the continuous varaible.

decimals

Number of decimal places for means and standard deviations or standard errors.

p.decimals

Number of decimal places for p-values. If a vector is provided rather than a single value, number of decimal places will depend on what range the p-value lies in. See p.cuts.

p.cuts

Cut-point(s) to control number of decimal places used for p-values. For example, by default p.cuts is 0.1 and p.decimals is c(2, 3). This means that p-values in the range [0.1, 1] will be printed to two decimal places, while p-values in the range [0, 0.1)

p.lowerbound

Controls cut-point at which p-values are no longer printed as their value, but rather

p.leading0

If TRUE, p-values are printed with 0 before decimal place; if FALSE, the leading 0 is omitted.

p.avoid1

If TRUE, p-values rounded to 1 are not printed as 1, but as >0.99 (or similarly depending on values for p.decimals and p.cuts).

n

If TRUE, the table returned will include sample sizes in the column headings.

se

If TRUE, the table will present mean (standard error) rather than mean (standard deviation).

Value

• A character matrix with the requested frequency table. If you click on the matrix name under "Data" in the RStudio Workspace tab, you will see a clean table that you can copy and paste into a statistical report or manuscript. If latex is set to TRUE, the character matrix will be formatted for inserting into an Sweave or Knitr report using the xtable package [1].

Details

If x has two levels, a t-test is used to test for a difference in means. An F test is first used to determine whether the equal variance or unequal variance t-test is appropriate. If x has more than two levels, a one-way analysis of variance is used to test for a difference in means across the groups. Both x and y can have missing values. The function drops observations with missing x or y.

References

1. Dahl DB (2013). xtable: Export tables to LaTeX or HTML. R package version 1.7-1, http://CRAN.R-project.org/package=xtable. Acknowledgment: This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-0940903.

See Also

tabfreq tabcox tabglm tabgee

Examples

# Load in sample dataset d and drop rows with missing values
data(d)
d <- d[complete.cases(d),]

# Create labels for group and race
groups <- c("Control", "Treatment")
races <- c("White", "Black", "Mexican American", "Other")

# Compare mean BMI in control group vs. treatment group
meanstable1 <- tabmeans(x = d$group, y = d$bmi, xlevels = groups, yname = "BMI")

# Compare mean BMI by race and include sample size
meanstable2 <- tabmeans(x = d$race, y = d$bmi, xlevels = races, yname = "BMI", n = TRUE)

# Create single table comparing mean BMI and mean age in control vs. treatment group
meanstable3 <- rbind(tabmeans(x = d$group, y = d$bmi, xlevels = groups, yname = "BMI"),
                     tabmeans(x = d$group, y = d$age, xlevels = groups, yname = "Age"))

# Click on meanstable1, meanstable2, and meanstable3 in the Workspace tab of RStudio 
# to see the tables that could be copied and pasted into a report or manuscript. 
# Alternatively, setting the latex input to TRUE produces tables that can be inserted 
# into LaTeX using the xtable package.