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Statistics Module 7 Statistics • Tool to help us see and interpret what we might miss • Descriptive Statistics • Inferential Statistics Descriptive Statistics • Numerical data used to measure and decide characteristics of groups Measures of Central Tendency • Mean • Average score • Extreme scores have the greatest impact on mean • Most common • Median • Midpoint, equal # of scores on either side • Mode • Most frequently occurring score in a distribution Let’s practice • 1, 1, 3, 4, 5, 5, 5, 10 • Mean • Median • Mode Measures of Variation • A measure of variation is a single score that presents information about the spread of scores in a distribution. • Range – highest score minus the lowest score – 95 – 35 = 60 Measures of Variation • Standard deviation • A standard measurement of how much the scores in a distribution deviate from the mean • Most widely used Measures of Variation • Normal distribution • Normal curve – bell-shaped • In a normal distribution of test scores, the percentage of scores that fall at or above the mean score is 50. • All score-based normal curves have the following 6895-99.7 rule in common. – 68% fall within one standard deviation of mean – 95% fall within two standard deviations of mean – 99.7% fall within three standard deviations of mean Skewed deviations • Positively skewed distributions – More scores on the low end of scale – Median is a better rep of central tendency – Looks like a “P” lying on its back Skewed deviations • Negatively skewed distributions – More scores on the high end of scale – Median is a better rep of central tendency Inferential Statistics • Most experiments are conducted with a small sample • Want to generalize the results from their small sample to a larger population • Used to determine how likely it is that a study’s outcome is due to chance and can it really be generalized to the larger population