Stat Unit 3--Winter 2008

Stat Unit 3--Winter 2008 - • Central Tendency –...

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Unformatted text preview: • Central Tendency – Where’s the middle, what’s typical in a distribution? • Mode – Most frequently occurring category » Nominal data • Median – Value of the middle case when distribution is ranked » Ordinal data • Mean – Arithmetic average » Sum of case values divided by number of cases » Interval/ratio data • Variability – Once we know something about the center of a distribution, next question is • To what degree do cases tend to be different or vary from this measure of the center Number of Children 5 10 15 20 25 30 4 8 1 2 1 6 2 2 4 2 8 3 2 3 6 4 4 4 4 9 5 3 5 7 6 1 6 5 Age • Here’s a graph of the variability in age of students in a first grade class • Variability is very small • Here’s a graph of EMU students by age • More variability than first grader example Number of Students 500 1000 1500 2000 2500 3000 3500 4000 4 8 1 2 1 6 2 2 4 2 8 3 2 3 6 4 4 4 4 9 5 3 5 7 6 1 6 5 AGE Number of People 200 400 600 800 1000 1200 4 8 1 2 1 6 2 2 4 2 8 3 2 3 6 4 4 4 4 9 5 3 5 7 6 1 6 5 + Age • Finally, here’s a graph of population of Ypsilanti by age • There is considerably more variability here – Measures of variability depend on the level of measurement of the variable or attribute • Nominal data – Index of Qualitative Variation (IQV) is available » Rarely used • Ordinal data – Range and interquartile range • Interval/ratio data – Standard deviation •...
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Stat Unit 3--Winter 2008 - • Central Tendency –...

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