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Bell Curve Basics

Updated on March 14, 2017

What is a Bell Curve? Well, basically it's a chart that plots the standard deviation of data. It can tell you both the mean and the extremes of related information like the range of temperatures over the length of a year, a sampling of how many calories people eat in a day, or the surface temperatures of a thousand stars. The plotting of that data usually comes out looking like a bell-shaped curve.


FAQ About the Bell Curve

The Bell Curve? Wasn't that a book once? That's right; The Bell Curve was a controversial book by Richard Herrnstein and Charles Murray which discussed the source of human intelligence and its impact on both society and individual human success. It's been out of print for a while and the name comes from the bell curve that represents the normal distribution of Intelligence Quotient (IQ) scores in a population.

What is Standard Deviation? Standard deviation can help you get a more clear picture of the meaning behind the data. It gives you a spread of the values and can help you get an idea of the normal distribution of data, in which most of the data points are going to be slightly above or slightly below the average. There will probably be a few data points on the extreme ends.

Is there a way I can calculate the standard deviation without manually making a bell chart? Sure there is. If you happen to have a spreadsheet full of data in Excel, you can ask it to do it for you by entering something =STDEV(A1:Z99). Just customize your standard deviation by replacing the A1 with the upper-left cell and the Z99 with the lower-right cell in your range. You can also calculate the standard deviation on your own by adding up the values in your sample, dividing by the number of samples to get the mean, and then subtracting the mean from each individual value, squaring the result, and then adding up all those values, dividing them to get the mean of those, and then taking the square root of that mean. The number you get is your standard deviation. That's a lot of work for a standard deviation, isn't it? Luckily, a quick search on Google will give you a few calculators you can use to do the job for you.

What do the X-axis and the Y-axis represent in a bell curve? The X-axis usually deals with the value under consideration. It can be a variety of things from the number of cattle on the polled farms to the IQ range of a population. The Y-axis usually deals with the number of samples that had a particular value along the X-axis. Because most samples tend to fall somewhere in the middle, the chart tends to take on the bell-like curve it gets its name from.

Bell Curves in Everyday Life

You might be wondering if bell curves can be used in your everyday life. Well, if your work or life has anything at all to do with statistics, they can be very practical for determining what a normal range of data might look like. They're a good way to track anything from price ranges to the number of eggs you get from each individual chicken in your flock and compare it to the mean. If you have a website and keep an eye on your traffic, you probably keep a mental bell chart in your head and know at a glance when your traffic is way down because Google reorganized its search algorithm or facing a surge because some nice person posted a link on their popular blog. So bell curves are very useful for a lot of matters having to do with numbers and statistics in everyday life.


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    • Marcy Goodfleisch profile image

      Marcy Goodfleisch 5 years ago from Planet Earth

      I really appreciate this article - I recently downloaded the e-version of The Bell Curve (it is now on Kindle!), and this is helpful for understanding the meaning of the statistical variations. Thanks!

      Voted up!

    • MG Singh profile image

      MG Singh 5 years ago from Singapore

      So nice to have a professional article on science from the plethora of food and drink articles.