Probability: Normal Distribution (Notes)

in #mathematics7 years ago (edited)

In this video I go over a brief introduction on the most commonly used probability density function, the normal distribution. This function is represented by a bell-shaped curve, often referred to as the Bell Curve, and models many natural phenomena well, such as test scores, rainfall, heights, weights, etc. Although I go over the basics of the normal distribution function and its properties in terms of the standard deviation, I leave the actual derivation of the formula to later videos, as it is more advanced. So stay tuned for those videos!


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Applications of Integrals: Probability: Normal Distributions

Many important random phenomena are modeled by a normal distribution (or as described in my earlier videos, as a Bell Curve).

  • Examples are:
  • test scores on aptitude tests
  • heights and weights of individuals from a homogeneous population
  • annual rainfall in a given location

This means that the probability density function of the random variable X is a member of the family of functions:

Where:

  • μ is the mean or average
  • σ is the standard deviation
    • σ is the lowercase Greek letter sigma.

The standard deviation is a measure of how spread out the values of X are.

From the bell-shaped graphs of the members of the family in the figure below, we see that for small values of σ the values of X are clustered about the mean, whereas for larger values of σ the values of X are more spread out.

Statisticians have methods for using sets of data to estimate μ and σ.

The factor

is needed to make the f a probability density function.

In fact, it can be verified using the methods of multivariable calculus that:

I will prove this formula and that μ is indeed the average, as well how the normal distribution formula was derived in later videos so stay tuned!