Measures of Central Tendency

Mode
Most frequently occurring score.
Median
The number
or score that divides a distribution in half. 50% of a distribution's scores will fall above the
median, and 0% will fall below the median.
Mean
Calculated by summing the set of scores and
dividing by "n". The most useful measure of central tendency. Symbols: Sample = xbar;
Population = µ
Measures of Variability

Variance
The mean of the squared deviations from the mean of a
distribution. Symbols: s
2
=sample variance; r
2
= population variance
Standard Deviation

The square root of the variance. Symbols: s = sample standard deviation; σ
= population standard deviation. The most useful measure of variability. More interpretable than
variance because it’s in the original units of measurement
Sampling
We can’t measure every person in a given population that is of interest to us: Pickup
truck owners in Texas. All college students in UTSA. All Possible customers for new products.
Every patient with a particular disease. This would be too expensive and would take too much
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 Spring '08
 Mendez
 Statistics, Normal Distribution, Standard Deviation

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