describe.by function

Basic summary statistics by group

Report basic summary statistics by a grouping variable. Useful if the grouping variable is some experimental variable and data are to be aggregated for plotting. Partly a wrapper for by and describe

describeBy(x, group=NULL,mat=FALSE,type=3,digits=15,data,...)
describe.by(x, group=NULL,mat=FALSE,type=3,...)  # deprecated

Arguments

• x: a data.frame or matrix. See note for statsBy.
• group: a grouping variable or a list of grouping variables. (may be ignored if calling using the formula mode.)
• mat: provide a matrix output rather than a list
• type: Which type of skew and kurtosis should be found
• digits: When giving matrix output, how many digits should be reported?
• data: Needed if using formula input
• ...: parameters to be passed to describe

Details

To get descriptive statistics for several different grouping variables, make sure that group is a list. In the case of matrix output with multiple grouping variables, the grouping variable values are added to the output.

As of July, 2020, the grouping variable(s) may be specified in formula mode (see the examples).

The type parameter specifies which version of skew and kurtosis should be found. See describe for more details.

An alternative function (statsBy) returns a list of means, n, and standard deviations for each group. This is particularly useful if finding weighted correlations of group means using cor.wt. More importantly, it does a proper within and between group decomposition of the correlation.

cohen.d will work for two groups. It converts the data into mean differences and pools the within group standard deviations. Returns cohen.d statistic as well as the multivariate generalization (Mahalanobis D).

Returns

A data.frame of the relevant statistics broken down by group:

item name

item number

number of valid cases

mean

standard deviation

median

mad: median absolute deviation (from the median)

minimum

maximum

skew

standard error

Author(s)

William Revelle

See Also

describe, statsBy, densityBy and violinBy, cohen.d, cohen.d.by, and cohen.d.ci

as well as error.bars and error.bars.by for other graphical displays.

Examples

data(sat.act)
describeBy(sat.act,sat.act$gender) #just one grouping variable
describeBy(sat.act ~ gender)   #describe the entire set formula input
describeBy(SATV + SATQ ~ gender,data =sat.act)  #specify the data set if using formula
#describeBy(sat.act,list(sat.act$gender,sat.act$education))  #two grouping variables
describeBy(sat.act ~ gender +  education) #two grouping variables
des.mat <- describeBy(age ~ education,mat=TRUE,data = sat.act) #matrix (data.frame) output 
des.mat <- describeBy(age ~ education + gender, data=sat.act,
               mat=TRUE,digits=2)  #matrix output  rounded to 2 decimals