Ch4_Central Tendency

Ch4_Central Tendency - Chapt er 4 M easur es of Cent r al...

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Chapter 4 Measures of Central Tendency
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Descriptive Statistics Measures of: 1. Central tendency (typical score) Mode, Median, Mean. 1. Variability (amount of variability) Range, Variance, Standard deviation.
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Mode The most frequently occurring score Unimodal : distribution has only one hump. Bimodal : distribution has two humps. Multimodal : distribution has more than 2 humps. Mode(s) is (are) the “biggest” hump(s).
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Mode Not a stable measure of central tendency. Not affected by extreme scores. Can be used with nominal, ordinal, or interval data (e.g. religious affiliation as nominal data).
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Example Six patients in a psychiatric ward were observed and the number of times each patient requested assistance from the nursing staff during a 24-hour period was recorded.
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What is the Mode? Patient Number of requests 1 3 2 4 3 0 4 7 5 2 6 4
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Example Here are the ages in years of the cars worked on by the Village Autohaus last week : 5, 6, 3, 6, 11, 7, 9, 10, 2, 4, 10, 6, 2, 1, 5 What is the mode of the data?
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Median The score that has an equal number of scores above and below it (the 50th percentile). It cuts the distribution into two equal parts. Position of median = (N+1)/ 2
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To Find Median: For odd number of scores with no tie numbers around the median: Arrange data (ordinal or interval) in order of size - the middlemost point in the distribution is the median.
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Example The number of times 5 patients requested pain killers following a wisdom tooth extraction: 1, 3, 4, 5, 9 What is the median?
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This note was uploaded on 11/30/2009 for the course HP 400m at USC.

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Ch4_Central Tendency - Chapt er 4 M easur es of Cent r al...

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