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Statistics 101 Measures of Central Tendency • Mean - Average • Median - Middle • Mode Most Common - How many cookies did you eat last week? 22 6 Mean 100 15 18 1 30 6 22+6+100+15+18+1+30+6+6 = 204 204/9 = 22.66 Median 1 6 6 6 15 18 22 30 100 Mode 1 - one instance 6 - three instances 15 - one instance 18 - one instance 22 - one instance 30 - one instance 6 The Normal Curve • Standard Deviation • Variation from the mean (or another point) • % of scores in a distribution that fall above/below a given score. Standard Deviation To calculate the Variance, take each difference, square it, and then average the result And the Standard Deviation is just the square root of Variance, so: Standard Deviation lets us know what’s normal or average. Scatterplots Perfect positive correlation (+1.00) Scatterplot is a graph that comprises of points generated by values of two variables. The slope of points depicts the direction, The amount of scatter shows the strength of relationship. Scatterplots Perfect negative correlation (-1.00) No relationship (0.00) Scatterplot on the left shows a relation between the variables, and the one on the right shows no relationship between the two variables. Correlation Coefficient Value of r Strength of Relationship -1.0 to -0.5 or 1.0 to 0.5 STRONG -0.5 to –0.3 or 0.3 to 0.5 Moderate -0.3 to –0.1 or 0.1 to 0.3 Weak –0.1 to 0.1 None or very weak Percentile Rank