basic descriptive statistics using r(2)

8/8/2019 Basic Descriptive Statistics Using R(2)

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Last Modified January 26, 2007

Basic Descriptive Statistics Using R

In the following handout words and symbols in bold are R functions and words and

symbols in italics are entries supplied by the user; underlined words and symbols areoptional entries (all current as of version R-2.4.1). Sample texts from an R session are

highlighted with gray shading.

Measures of Central Tendency

mean(object) provides the mean of the objects elements

> quarters = c(5.683, 5.620, 5.551, 5.549, 5.536,

+ 5.552, 5.548, 5.539, 5.554, 5.552, 5.684, 5.632

> mean(quarters)

[1] 5.583333

median(object) provides the median of the objects elements

> median(quarters)

[1] 5.552

mode there is no built in function for finding an objects mode; however, the

command table(object) creates a frequency table for the objects elements and themode is the element in this table with the greatest frequency

> table(quarters)

5.536 5.539 5.548 5.549 5.551 5.552 5.554 5.62 5.632 5.683 5.684

1 1 1 1 1 2 1 1 1 1 1

midrange there is no built in function for reporting the midrange; the command

shown below use the functions for an objects maximum (max) and minimum (min)to calculate and print the objects midrange

> midrange = (max(quarters) + min(quarters))/2; midrange

[1] 5.61

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Measures of Spread

var(object) provides the sample variance of the objects elements

> var(quarters)

[1] 0.003116606

sd(object) provides the sample standard deviation of the objects elements

> sd(quarters)

[1] 0.05582657

standard error of the mean there is no built in function for reporting the standard

error of the mean; the command shown below use the functions for the objects

standard deviation (sd) and number of elements (length), as well as the mathematicalfunction for finding a square root (sqrt) to calculate and print the objects standard

error of the mean

> sem = sd(quarters)/sqrt(length(quarters)); sem

[1] 0.01611574

range there is no built in function for reporting the range; the command shown

below use the functions for an objects maximum (max) and minimum (min)

elements to calculate and print the objects range

> range = (max(quarters) min(quarters)); range

[1] 0.148

IQR(object) provides the objects interquartile range; note this value may differslightly from that provided by other programs because there is no single accepted

definition for FU and FL

> IQR(quarters)

[1] 0.07425

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Quantitative and Visual Representations of a Distributions Shape

skew(object) provides the skewness for an object; this function is not included in R,but is available from the file skew&kurt.RData, which is available on the courses

I-drive account.

> skew(quarters)

[1] 0.8508155

kurt(object) provides the kurtosis for an object relative to that of a normal

distribution; this function is not included in R, but is available from the file

skew&kurt.RData, which is available on the courses I-drive account.

> kurt(quarters)

[1] -1.075001

hist(object) creates a histogram of the objects elements with the number of

compartments chosen by R.

> hist(quarters)

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boxplot(object 1, object 2, names, horizontal= TRUE) creates a boxplot of theobjects elements (for multiple objects, a boxplot is drawn for each); names is a

vector containing the names of the objects, which adds labels on the x-axis when

plotting more than one boxplot. Setting horizontal to TRUE (the default value isFALSE) creates a horizontal boxplot.

> boxplot(quarters)

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basic descriptive statistics using r(2)

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