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Week 3 Study Notes

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Damian Dupuy
Study Guide

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GGR 270 Lecture 3 September 29, 2010
Statistics vs. Parameters
Graphs are limited in what they can tell us
Difficulty making inferences about a population when looking at a subset or sample
Therefore, we need to use numerical measures
Measures associated with the population are called parameters
Measures associated with a sample are called statistics
Measures of the centre
Most commonly used measure of central tendency
Sum of all values or observations divided by the number of observations
Sample Population
Value occupying the middle position in an ordered set of observations
Order the observations, lowest to highest, and find the middle position
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Expressed as: .5(n+1)
Value that occurs with the highest frequency
Allows you to locate the peak of relative frequency histogram
Choosing appropriate measure
Mean is usually the best measure as it is sensitive to change in a single observation
Not a good measure when:
Distribution is bimodal
Skewed distribution
Outliers (extreme values) are present in the data set
Mean, Median, Mode
Mode, Mean, Median, Mode
Positive skew
mode, med, mean mean>median
Negative skew
mean, median, mode mean<median
*Mean always dragged in direction of skew
Measures of dispersion
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