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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