Website Usability Guidelines

Website Usability Basics

Crunching the Numbers - When you're ready, you'll need to do some number crunching. Although a discussion of statistical methods could easily fill several books, there are at minimum a handful of important calculations to make for each site:

• Mean: The mean is derived by adding all values in a set and dividing by the number of items in the set. For example, in a data set comprising scores of 3, 4, 4, 5, 3, 2 and 5, the mean would be 26 / 7, or 3.72.
  
  
• Median: The median is derived by lining up all values in a data set from smallest to largest and picking the one that's right in the middle. To continue our example, in a data set comprising values of 2, 3, 3, 4, 4, 4 and 5 the median would be 3.5 (with an odd number of values, split the two around the middle). Some feel that the median is a better representation of an average score, but I think that using both the mean and the median give you a better overall picture.
  
  
• Mode: The mode is derived by calculating the highest frequency value in a data set. In our example data set, the mode would be 4 (there are more 4s than any other value).
  
  
• Maximum, minimum, and spread: The maximum value in a data set is the largest value, and the minimum value is the smallest. The spread is the difference between these two values. To complete our example, the minimum value is 2 the maximum value is 5 and the spread is 3.

Together, these values (mean, median, mode, maximum value, minimum value, and spread) start to tell a story.

They don't tell the whole story, but they certainly illustrate and make plain the results of your work. For example, websites that have means and medians that are far apart indicate more weight on extreme ends of the scale (either more 1s or 5s in the established rating system).