stats ch2 mean, sd, z-scores

# stats ch2 mean, sd, z-scores - The Mean Variance and...

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The Mean, Variance, and Standard Deviation The primary numbers used to describe a distribution of scores when not using a picture.

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Mean The mean is an average score known as a measure of central tendency . The mean is used to represent a whole set of data with one number. The mean is the single best value for this purpose.
The Mean – M The mean need not represent an actual, or even a possible value on a variable. The mean uses all the scores in its calculation and is very sensitive to (affected by) extreme scores called outliers. M = ( Σ X)/N ( Σ means sum up, X means all the scores, N is the total number of scores).

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In addition to being the best possible single value representation of a set of data, it is also our best prediction for an individual score if we have no other information available.
Calculate the mean number of children for our sample. Each family’s score is an X. 0 2 3 1 1 1 2 0 2 2 4 8 Σ X = 0+2+3+1+1+1+2+0+2+2+4+8 = 26 N = 12 M = 26/12 = 2.17

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Other measures of central tendency The median – the middlemost score in a set of ordered scores. Good when a few extreme scores would greatly affect the mean. The mode – the most frequently occurring score in a set of scores. Not affected by a few extreme scores. Good for nominal (qualitative, categorical) variables.
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## This note was uploaded on 10/12/2008 for the course PSY 385 taught by Professor Mannes during the Fall '08 term at Widener.

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stats ch2 mean, sd, z-scores - The Mean Variance and...

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