Synonymous with the normal curve; the distributions of events in a bell-shaped curve. This is similar to the sigmoid curve that is derived mathematically but applies to many situations. It indicates there is generally a majority in the middle with extremes at either end. Here the actual number of events is used, where in the sigmoid curve it is the rate of change. Common examples are the distribution of grades in a class. (1) or the outcomes of a random event, like the number of heads in a series of coin tosses. Normal Probability density function The normal distribution, also called Gaussian distribution, is an extremely important probability distribution in many fields. It is a family of distributions of the same general form, differing in their location and scale parameters: the mean ("average") and standard deviation ("variability"), respectively. The standard normal distribution is the normal distribution with a mean of zero and a standard deviation of one (the green curves in the plot above). It is often called the bell curve because the graph of its probability density resembles a bell. Equivalent ways to specify the normal distribution are: the moments, the cumulants, the characteristic function, the moment-generating function, and the cumulant-generating function. All of the cumulants of the normal distribution are zero, except the first two.
