Know the properties of the mean and median and how these measures are or are not affected by skew. These are not the same quantity. 1.When using the computational formula for the standard deviation, use all of the raw scores, even if a particular score occurs more than once. 1.When calculating the standard deviation, divide the sum of squares by N first and then take the square root of the outcome. Sum of squares, standard deviation, and variance are never negative values.
Z scores can be negative.
Be sure to use a negative sign. 1.If you calculate r and it is greater than 1 or less than -1, you have done something wrong. Find two points that are on the line by plugging in two values of x, and draw the line through them. 1.Be sure you know how to calculate confidence intervals for regression predictions, and know what the role of the standard error of estimate is in predicting new scores from a regression equation. Then determine whether the problem requires the addition or multiplication rule, and whether the events involved are independent or dependent, and mutually exclusive or not mutually exclusive.