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What we will learn
Know your problem
3. Typical questions about change over time
Know your data
Visualize your data - bar chart
Work with your chart
Check yourself


We've identified a few situations where we might want to see change over time. The following questions will help us draw correct conclusions about observed changes over time. We'll start with general questions:

  • Is there a general tendency for this data?
  • If so, what is it?
  • Are values constantly increasing? Decreasing? Stable?
  • Or does this data display no general tendency?

Once we have the overall "feel" of our data, we can ask questions that are more specific to that set of information, such as:

  • What is the minimum value? When did it occur?
  • What is the maximum value? When did it occur?
  • What is the difference between the maximum and minimum values? How much time passed between these two points?
  • What is the typical range of changes in this data?
  • Was there a periodic fluctuation (i.e. any marked and repeating change in pattern)? For example, was there noticeable growth every Tuesday?
  • How did values evolve from time period to time period (e.g. from month to month)? Was this change stable? Or did values increase and then decrease?