Presentation Transcript
Descriptive Statistics: Descriptive Statistics Chee-Wee Tan Module P1112
What are descriptive statistics?: What are descriptive statistics? Summarising data
Spotting patterns
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Case Study: Case Study Drink kryptonite --ïƒ More push-ups? 1 6 1 2 6 1 2 2 10 3 4 9 4 5 7 5 6 6 6 2 6 6 9 7 7 8 8 9 9 3 3 10 2 1 10 2 10 10 10 6 6 6 9
Histogram: Histogram
Distributions: Distributions Normal Distribution
Skewed Distributions: Skewed Distributions Positively skewed Negatively skewed
Kurtosis: Kurtosis Leptokurtic distribution platykurtic distribution
Measures of Central Tendencies: Measures of Central Tendencies Mode
Used with nominal data
Bimodality may be messy to deal with.
Measures of Central Tendency: Measures of Central Tendency Median
1 1 1 1 2 2 2 2 2 2 3 3 3 4 4 5 5 6 6 6 6 6 6 6 6 6 6 7 7 7 8 8 9 9 9 9 9 10 10 10 10 10 10
Measures of Central Tendency: Measures of Central Tendency Mean
Can be used in interval and ratio data
Measures of Dispersion: Measures of Dispersion Range
60%
Measures of Dispersion: Measures of Dispersion How much cleverer am I?
Squaring deviations: Squaring deviations 42 = 16 (- 4)2 = 16
Add up all (deviations)2
Number of scores we have (N)
= Variance
(N-1) used to divide instead of N
Field A. (2003) How to Design & Report Experiments’, Sage Publications, London, p129.
Standard Deviation: Standard Deviation Push-up squared?
Square-root of variance = standard deviation
Presenting our statistics: Presenting our statistics The mean number of push-ups for kryptonite drinkers is 5.7 push-ups (S.D. = 3.01)
Or,
Non-kryptonite drinkers did less number of push-ups (M = 2.0, S.D. = 2.7) than kryptonite drinkers (M = 5.7, S.D. = 3.01).
Presenting our statistics: Presenting our statistics Or we could portray this information using a graph, something like this…
Summary: Summary Distributions
Measures of central tendency
Measures of dispersion
Using graphs
Remember to read the directed reading!