also as student's distribution; t distribution is a specific type of symmetric(bell-shaped) distribution with a lower height and a wider spread(or larger standard deviation) than the standard normal distribution . However, as the sample size becomes larger, the t distribution approaches the standard normal distribution. The total area under a t distribution curve is 1.0 or 100 percent. It has only one parameter, called the degrees of freedom(df). The mean of it is equal to 0, the df is equal to the sample size minus one, that is, df = n -1.
