The term bell curve is employed to explain the mathematical concept called Gaussian distribution , sometimes mentioned as normal distribution . "Bell curve" refers to the bell that's created when a line is plotted using the info points for an item that meets the standards of Gaussian distribution .

In a bell curve, the middle contains the best number of a worth and, therefore, it's the very best point on the arc of the road . This point is mentioned the mean, but in simple terms, it's the very best number of occurrences of a component (in statistical terms, the mode).

Normal Distribution

The important thing to note about a normal distribution is that the curve is concentrated in the center and decreases on either side. This is significant therein the info has less of a bent to supply unusually extreme values, called outliers, as compared to other distributions. Also, the bell curve signifies that the data is symmetrical. This means that you simply can create reasonable expectations on the likelihood that an outcome will lie within a variety to the left or right of the middle , once you have measured the quantity of deviation contained within the data.This is measured in terms of ordinary deviations.

A bell curve graph depends on two factors: the mean and the standard deviation. The mean identifies the position of the middle and therefore the variance determines the peak and width of the bell. For example, an outsized variance creates a bell that's short and wide while alittle variance creates a tall and narrow curve.

Bell Curve Probability and Standard Deviation

To understand the probability factors of a traditional distribution, you would like to know the subsequent rules:

The total area under the curve is equal to 1 (100%)

About 68% of the world under the curve falls within one variance .

About 95% of the world under the curve falls within two standard deviations.

About 99.7% of the area under the curve falls within three standard deviations.

Items 2, 3, and 4 above are sometimes referred to as the empirical rule or the 68–95–99.7 rule. Once you identify that the info is generally distributed (bell curved) and calculate the mean and variance , you'll determine the probability that one datum will fall within a given range of possibilities.

Bell Curve Example

A good example of a bell curve or Gaussian distribution is that the roll of two dice. The distribution is centered round the number seven and therefore the probability decreases as you progress faraway from the middle .

Here is that the percent chance of the varied outcomes once you roll two dice.

Two: (1/36) 2.78%

Three: (2/36) 5.56%

Four: (3/36) 8.33%

Five: (4/36) 11.11%

Six: (5/36) 13.89%

Seven: (6/36) 16.67% = most likely outcome

Eight: (5/36) 13.89%

Nine: (4/36) 11.11%

Ten: (3/36) 8.33%

Eleven: (2/36) 5.56%

Twelve: (1/36) 2.78%

Normal distributions have many convenient properties, so in many cases, especially in physics and astronomy, random variations with unknown distributions are often assumed to be normal to permit for probability calculations. Although this will be a dangerous assumption, it's often an honest approximation thanks to a surprising result referred to as the central limit theorem.

This theorem states that the mean of any set of variants with any distribution having a finite mean and variance tends to occur during a Gaussian distribution . Many common attributes like test scores or height follow roughly normal distributions, with few members at the high and low ends and lots of within the middle.

When You Shouldn't Use the Bell Curve

There are some sorts of data that do not follow a traditional distribution pattern. These data sets should not be forced to undertake to suit a bell curve. A classic example would be student grades, which frequently have two modes. Other sorts of data that do not follow the curve include income, increase , and mechanical failures.