There are four graphs; a histogram, a box plot, an average value per time-of-day, and an average value per day-of-week.
A histogram is a graphical display of frequencies, shown as bars. It shows what proportion of cases fall into each of several categories. In this case, it shows how many values have fallen into each of ten ranges, starting with 1-9, then 10-19, 20-29, and so forth.
John Tukey described the Box Plot in 1977 as an efficient method for displaying a data summary. It visually summarizes the median, the upper and lower quartiles, and the minimum and maximum data values. The filled box itself contains the middle 50% of the data. The right edge (hinge) of the box indicates the 75th percentile of the data set, and the lower hinge indicates the 25th percentile. The range of the middle two quartiles is known as the inter-quartile range. The line inside the box indicates the median value of the data. If the median line within the box is not equidistant from the hinges, then the data is skewed. The ends of the horizontal lines or "whiskers" indicate the minimum and maximum data values, unless outliers are present in which case the whiskers extend to a maximum of 1.5 times the inter-quartile range. The points outside the ends of the whiskers are outliers or suspected outliers.
Values per Time-of-Day
This is a custom chart allowing you to view the average value for each of the 24 hours in a day. This might be useful for a variable that changes a lot during a typical day. For example, if you are tracking hunger, you might expect the hours before lunch and dinner to have the highest average value. Or, stress might be generally higher during working hours.
Values per Day-Of-Week
This is a custom chart allowing you to view the average value for each of the 7 days in a week. This can be useful for detecting factors that are dependent on the day; for example, your stress levels just might be lower on weekends. The first day of the week for this chart is Sunday.
Copyright 2009 by Mike Berro. All rights reserved.