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Chapter4.docx
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University of Toronto St. George
Psychology
PSY201H1
Kristie Dukewich
Fall
Description
PSY201H1: Chapter 4 Review Notes
 A characteristic of frequency distribution and its derivatives would be that it
does not allow quantitative comparisons to be made between two or more
distributions.
 The measure computed (of the average score of each variable) is a measure
of the central tendency of each distribution.
 It is important and useful to quantify the variability of the distribution.
 Central tendency and variability are the most important factors, and the two
characteristics of distribution which are typically quantified.
Measures of Central Tendency
Arithmetic Mean
 Value originally calculated when you average something.
 The sum of the scores divided by the number of scores
 Key properties of the mean include the fact that it is sensitive to the exact
value of all the scores in the distribution. Any change in the scores will cause
a change in the mean.
 The sum of the deviations about the mean equals zero. Algebraically:

 The mean is also very sensitive to extreme scores (Extreme scores: Score that
is far from the mean score)
 The sum of the squared deviations of all the scores about their mean is a
minimum. Algebraically:
 Of the measures used for central tendency, the mean is least subject to
sampling variation.
Overall Mean
 Often known as the weighed mean.
 Typically represented algebraically as: Median
 Defined as the scale value below which 50% of the scores fall.
 The median is the centermost score if the number of scores is odd. If the
number is even, the median is taken as the average of the two centermost
scores.
 The median is also
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