T-Distribution

• t-Distribution is used with small samples taken from population that is approximately normal.
• t-statistic (t-score) uses the sample deviation especially when the

  population variance is unknown.
• t-statistic is used when n<30 or when the population standard deviation

  is unknown.
• Degree of freedom - The number of values that are free to vary in a data set
• T-distribution is symmetric about the mean.
• The T-distribution stretches towards positive and negative

  infinities, and it never has a value less than 0.
• The area under the curve bound by two t-scores is equal

  to the probability that the t-score will fall within that area.
• The total area under any curves is equal to 1.
• The variance of the T-distribution is greater than one unit.