# Measures of position and variability

To produce the mean, median, minimum, maximum values, 1st and 3rd quartiles for maximum length, use

``````> summary(Maxle)
``````

To calculate the standard deviation for a variable:

``````> sd(Maxle, na.rm=TRUE)
``````

The `na.rm=TRUE` parameter is necessary because we have missing values in our measurements.

The boxplot is based on some of the values given by the `summary` function. Its central line represents the average mean. To produce a boxplot for maximum length:

``````> boxplot(Maxle)
``````

As above but for each material:

``````> tapply(Maxle,Mat,summary)
> boxplot(split(Maxle,Mat))
> tapply(Maxle,Mat,sd,na.rm=TRUE)
``````

Updated: