stat exam 1 - 1 DATA COLLECTION AND SUMMARIZATION...

DATA COLLECTION AND
SUMMARIZATION
Observational Study Terms
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Population: the entire group of interest
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Sample: a part of the population selected to
draw conclusions about the entire population
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Census: sample that attempts to include the
entire population.
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Parameter: concept that describes the
population (mean, median, std. dev, variance,
etc)
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Statistic: a number produced from the sample
that estimates a parameter
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Inferential statistics are used to make
generalizations about the real world from
sample data.
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Descriptive statistics describe data.
Experiment Terms
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Experimental group: A collection of
experimental units subjected to a difference in
treatment, imposed by the experimenter
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Control group: A collection of experimental
units subjected to the same conditions as those
in experimental group except that no treatment
is imposed.
Quantitative Data
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Typical: characterized by the center of the data
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Spread: reported as an interval containing most
of the data
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Symmetric: roughly the same mirror image on
each side of the center value
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Skewed data: data has one side much longer
than the other relative to the mode.
Statistics for quantitative data
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Median: middle observation if the values are
arranged in increasing order.
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Mean: average, given by:
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Inter-quartile range, IQR: Q3-Q1: the middle
50% of the data
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Sample variance, s
2
:
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Standard deviation, s: square root of sample
variance. Preferred because it has the same
units as the data.
o
Sample mean and st. deviation are good
measures of center and spread for
symmetric data
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If the data is skewed or has outliers, the sample
median and IQR are more commonly used.
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Outliers affect the mean more than the median.
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Right skewed: mode<median<mean
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Left skewed: mean<median<mode
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Summary Statistics
o
P
th percentile: the value such that
p*100% of the values are below it and (1-
p)*100% are above it.