experimental methods: statistics & correlation mr. koch ap psychology forest lake high school
TRANSCRIPT
Experimental Methods:Statistics & Correlation
Mr. KochAP Psychology
Forest Lake High School
Statistics
• Types:– Descriptive – describe data– Inferential – mathematical procedures that help
psychologists make inferences about what data mean
• Distributions:– Frequency distribution– Histogram– Percentile rank
Central Tendencies
• Mean (M) – arithmetic average(1122333444455555) = 56/16 = 3.5
• Median – halfway point in a set of data(1122333444455555) = middle #(s)
• Mode – score that occurs most frequently5 = most frequent #
Variation
• Range = gap between highest and lowest scores (5-1)
• Standard Deviation (SD)– Calculate each difference (deviation) between each
score and the mean– Square these deviations– Find their average– Find the square root of this average– Use a “normal curve” to interpret results
Standard deviation gauges whether scores are packed together or dispersed because it uses information from each score. (The true basis for curving a test.)
M = 160/4 = 40 Sum of (deviations)² = 46
SD = √{[sum of (deviations)²]/number of scores} = √(46/4) = 3.4
Test Scores Deviation from the Mean (40)
Deviation Squared
36 -4 16
38 -2 4
41 +1 1
45 +5 25
The Normal (aka Bell) Curve
Negatively skewed Bell Curve Positively skewed Bell Curve
Inferential Statistics
• Statistical significance • Calculation of the likelihood a result happens by chance• Most use 5% (arbitrary) as standard for determining
significant difference between meansp < .05
• Principles:– Representative samples are better than biased samples– More cases are better than fewer– Less variable observations are more reliable than highly
variable observation
Correlation• Scatter plot• Correlation coefficient
• r = +1.00 One set of scores goes up in direct proportion to the other
• r = 0.00 Scores unrelated
• r = -1.00 One set of
scores goes up as the other goes down
Examples• + (positive)– Child abuse / aggressiveness– Education / income– Studying / grades
• - (negative)– Self esteem / depression– Age / hours of sleep– Stress / health
• Correlation DOES NOT prove causation
• Only proves relationship, not cause and effect
Correlation
• “Illusory Correlations”:– A perceived correlation that really does not exist• Ex: lucky penny = wishes come true