PSY 203 Lecture Notes - Lecture 2: Level Of Measurement, Central Tendency, Normal Distribution
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Lecture 2 Descriptive Stats
Definitions
• Population - the complete set of individuals, objects, or scores that the investigator is interested
in studying.
• Sample - a subset of the population.
• Parameter - a numerical characteristic of the population.
• Statistic - a numerical characteristic of a sample.
Measures of Central Tendency
• Mean
o Average of your data
o Most stable measure of central tendency
o Can be used to infer info about the population
o It is sensitive to extreme scores in the distribution
o The sum of the deviations about the mean equals zero
o The mean is least subject to sampling variation
o In replications, the mean would be the most similar
o sum of deviations would equal to 0
• Median
o The middle value where 50% of the score fall above and 50% of the scores fall below
o Even value of scores
▪
= middle value
▪
= median
• Mode
o Most frequent number in the set of data
o Used when you have nominal data
Relationship between these three measures of Central Tendency
Normal Curve
Negatively skewed Distribution
Positively Skewed Distribution