Contingency Tables

The X² test of association (not to be confused with the X² goodness of fit) is used to test whether two categorical variables are independent or associated. If the p-value is low, it suggests the variables are not independent, and that there is a relationship between the two variables.

Usage

contTables(
  data,
  rows,
  cols,
  counts = NULL,
  layers = NULL,
  chiSq = TRUE,
  chiSqCorr = FALSE,
  likeRat = FALSE,
  fisher = FALSE,
  contCoef = FALSE,
  phiCra = FALSE,
  logOdds = FALSE,
  odds = FALSE,
  relRisk = FALSE,
  ci = TRUE,
  ciWidth = 95,
  gamma = FALSE,
  taub = FALSE,
  obs = TRUE,
  exp = FALSE,
  pcRow = FALSE,
  pcCol = FALSE,
  pcTot = FALSE,
  formula
)

Arguments

data

the data as a data frame

rows

the variable to use as the rows in the contingency table (not necessary when providing a formula, see the examples)

cols

the variable to use as the columns in the contingency table (not necessary when providing a formula, see the examples)

counts

the variable to use as the counts in the contingency table (not necessary when providing a formula, see the examples)

layers

the variables to use to split the contingency table (not necessary when providing a formula, see the examples)

chiSq

TRUE (default) or FALSE, provide X²

chiSqCorr

TRUE or FALSE (default), provide X² with continuity correction

likeRat

TRUE or FALSE (default), provide the likelihood ratio

fisher

TRUE or FALSE (default), provide Fisher's exact test

contCoef

TRUE or FALSE (default), provide the contingency coefficient

phiCra

TRUE or FALSE (default), provide Phi and Cramer's V

logOdds

TRUE or FALSE (default), provide the log odds ratio (only available for 2x2 tables)

odds

TRUE or FALSE (default), provide the odds ratio (only available for 2x2 tables)

relRisk

TRUE or FALSE (default), provide the relative risk (only available for 2x2 tables)

ci

TRUE or FALSE (default), provide confidence intervals for the comparative measures

ciWidth

a number between 50 and 99.9 (default: 95), width of the confidence intervals to provide

gamma

TRUE or FALSE (default), provide gamma

taub

TRUE or FALSE (default), provide Kendall's tau-b

obs

TRUE or FALSE (default), provide the observed counts

exp

TRUE or FALSE (default), provide the expected counts

pcRow

TRUE or FALSE (default), provide row percentages

pcCol

TRUE or FALSE (default), provide column percentages

pcTot

TRUE or FALSE (default), provide total percentages

formula

(optional) the formula to use, see the examples

Value

A results object containing:

results$freqs					a table of proportions
results$chiSq					a table of X² test results
results$odds					a table of comparative measures
results$nom					a table of the 'nominal' test results
results$gamma					a table of the gamma test results
results$taub					a table of the Kendall's tau-b test results

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

results$freqs$asDF

as.data.frame(results$freqs)

Examples

# \donttest{
# data('HairEyeColor')
# dat <- as.data.frame(HairEyeColor)

# contTables(formula = Freq ~ Hair:Eye, dat)

#
#  CONTINGENCY TABLES
#
#  Contingency Tables
#  -----------------------------------------------------
#    Hair     Brown    Blue    Hazel    Green    Total
#  -----------------------------------------------------
#    Black       68      20       15        5      108
#    Brown      119      84       54       29      286
#    Red         26      17       14       14       71
#    Blond        7      94       10       16      127
#    Total      220     215       93       64      592
#  -----------------------------------------------------
#
#
#  X² Tests
#  -------------------------------
#          Value    df    p
#  -------------------------------
#    X²      138     9    < .001
#    N       592
#  -------------------------------
#

# Alternatively, omit the left of the formula (`Freq`) if each row
# represents a single observation:

# contTables(formula = ~ Hair:Eye, dat)
# }