Wait! Didn’t we already talk about what a histogram is at least two or three times in two or three different ways? Absolutely! But now we’re asking you to really think about what a histogram is. Don’t worry, the answer will become clearer as you move through this activity.

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We talked in Module 1 that one of the weaknesses of a histogram is that it’s a snapshot in time. That means that a histogram only tells the story of the data at any one given point in time. Even histograms that deal with a frequency of an event over time have a limited scope (a week or a year).

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Here’s an example. Let’s say you looked at a histogram for the number of births per day in the United States in May 2002. The histogram obviously shows only May of 2002, but it doesn’t give you June or December. That means you could miss seasonal variations that give a more full picture of the frequency of births in the United States. You might also miss the overall trend by not looking at 2002-2012!

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When trends hold over an extended period of time, you can be sure that you’re seeing a pattern, not an event. Therefore, it is wise to explore multiple histograms over an extended period of time to gain useful knowledge about a process.

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A single histogram only tells one part of a long story.

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CRITICAL THINKING: How might you tell if a single histogram is sufficient or if multiple would be better to get a fuller story of the data?

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