The first step in examining the relationship between strength and job
performance is to look at some basic descriptive statistics for each
of the four variables. Measures of central tendency such as the mean
and the median
can be used to determine the location of the distribution of scores.
Measures of dispersion such as the range
(minimum, maximum), the standard
deviation, and the variance
tell you how spread out the scores were.
For the ARM test, we can see that the 147 study participants exerted an average
of 78.75 pounds of force. Half of the participants exerted less than
81.50 pounds of force while the other half scored greater than 81.50.
The scores were fairly spread out with a standard deviation of 21.11.
The lowest score was 19 lbs. Someone managed to exert a maximum score
of 132 lbs.
Another important step in evaluating a set of data is to look at
the overall shape of the distributions. One way of doing that is to
graph like the one below.
How many people exerted a force of 85 pounds?
Another good way to portray the shape of the distribution is with a
histogram as shown below.
Descriptive statistics and histograms for the remaining variables are
If the distribution were normal, between which two values would 68%
of the values lie?
The ratings variable:
appears to deviate from normality.
appears to approximately normally distributed.
Notice the distribution has a slight positive skew
(skewed to the right).