T DISTRIBUTION

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 .