Standard deviation

Standard deviation is a measurement of how values are spread around the mean. A high deviation means that there is a wide spread, whereas a low deviation means that the values are more tightly grouped around the mean. This measurement can be misleading if there is not a single focus point or there are numerous outliers.

We begin by showing a simple example using basic Java techniques. We are using our testData array from previous examples, duplicated here:

double[] testData = {12.5, 18.3, 11.2, 19.0, 22.1, 14.3, 16.2, 12.5,
   17.8, 16.5, 11.2}; 

Before we can calculate the standard deviation, we need to find the average. We could use any of our techniques listed in the Calculating the mean section, but we will add up our values and divide by the length of testData for simplicity's sake:

int sum = 0; 
for(double value : testData){ 
   sum += value; 
} 
double mean = sum/testData.length; 

Next, we create a variable, sdSum, to help us calculate the standard deviation. As...