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Types of Distributions - Normal

Types of Distributions - Normal

We'll cover the following...

4. Normal Distribution (Gaussian)

A normal distribution, the bell curve or Gaussian Distribution, is a distribution that represents the behavior in most situations. For example, exams scores are typically a bell curve where most students get the average score, C, a small number of students scores a B or a D, and an even smaller number scores an F or an A. This results in a distribution that looks like a bell:

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The bell curve is symmetrical, half of the data will fall to the left of the mean value and half will fall to the right of it.

Image Credits: https://www.mathsisfun.com
Image Credits: https://www.mathsisfun.com

Many things follow this type of spread, this is why this is used most often; you’d seen anywhere from businesses to academia to government. Here are some examples to give an idea of the variety covered by normal distributions:

  • Heights of people
  • Blood pressure
  • IQ scores
  • Salaries
  • Size of objects produced by machines

Some facts to remember about what percentage of our data falls within a certain number of standard deviations from the mean:

  • 68% of values are within 1 standard deviation of the mean
  • 95% of values are within 2 standard deviations of the mean
  • 99.7% of values are within 3 standard deviations of the mean
Image Credits: University of Virginia.
Image Credits: University of Virginia.

Why is it good to know standard deviations from the mean?

Because we can say the likelihood with which any value is:

  • likely to be within 1 standard deviation (68 out of 100 cases)
  • very likely to be within 2 standard deviations (95 out of 100 cases)
  • almost certainly
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