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A random variable normally distributed if the variable is continuous and the distribution is symmetric about mean. 50% observations lie below the mean and 50% observations lie above the mean. It has bell shaped continuous curve in which two parts of the made by the vertical line at mean exactly fit over each other. In this distribution mean = mode = median Variable representing normal distribution is a normal variable or normal variate. See chapter 4 for more details.
Standard Normal Distribution.
It is a normal distribution in which mean=mode=median=0 and standard deviation = 1. Variable representing standard normal distribution is a standard normal variable or standard normal variate. Standard normal variate is denoted by z.
Distribution involving only one variable is called as univariate distribution e.g. average marks obtained by students in an examination.
Distribution involving two one variables is called as bivariate distribution e.g. Marks obtained by students in two subjects say economics and statistics in an examination.
A distribution that is not symmetrical is skewed distribution.