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Overview: (t statistic used to test hypotheses about an unknown population…

- - - - Degrees of freedom - represent the number of score in a sample that are independent and free to vary.
        
        The greater the value of df for a sample, the better the sample variance represent the population variance, and the better the t statistic is close to the z-score.
        
        n-1 scores in a sample are independent and free to vary.
        
        The value of n-1 is called the degrees of freedom or df for the sample variance.
        
        A correlation is a measure between the two variables, X & Y.
        
        Pos (+) relationship means that X & Y vary in the same direction.
        
        Strength & Consistency
        
        The correlation numerical value measures the strength or consistency o the relationship.
        
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        Direction - The relationship between X & Y can be either positive or negative.
        
        Negative (-) relationship means X & Y are in opposite directions.
        
        The most common form of a relationship between X & Y is a straight line. There are times with special correlation exist for measuring and forms other correlations.
  - - - t distribution is a complete se of t values calculated for every possible random sample for a specific sample size (n) or specific df.
        
        The exact shape of the t distribution change with the df.
        
        For each possible number of the df it gets larger, the t distribution get closer in shape to a normal z-score distribution.
        
        The t distribution tends to be flatter an more spread out, whereas the normal z distribution has more of a central peak.