Department

GeographyCourse Code

GGR270H1Professor

Damian DupuyStudy Guide

FinalThis

**preview**shows page 1. to view the full**5 pages of the document.**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

Mean:

Most commonly used measure of central tendency

Sum of all values or observations divided by the number of observations

Sample Population

Median:

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)

Mode:

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

Normal

Mean, Median, Mode

Bimodal

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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