DATA COLLECTION AND
SUMMARIZATION
Observational Study Terms
•
Population:
the entire group of interest
•
Sample:
a part of the population selected to
draw conclusions about the entire population
•
Census:
sample that attempts to include the
entire population.
•
Parameter:
concept that describes the
population (mean, median, std. dev, variance,
etc)
•
Statistic:
a number produced from the sample
that estimates a parameter
•
Inferential statistics are used to make
generalizations about the real world from
sample data.
•
Descriptive statistics describe data.
Experiment Terms
•
Experimental group:
A collection of
experimental units subjected to a difference in
treatment, imposed by the experimenter
•
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
•
Typical:
characterized by the center of the data
•
Spread:
reported as an interval containing most
of the data
•
Symmetric:
roughly the same mirror image on
each side of the center value
•
Skewed data:
data has one side much longer
than the other relative to the mode.
Statistics for quantitative data
•
Median:
middle observation if the values are
arranged in increasing order.
•
Mean:
average, given by:
•
Inter-quartile range, IQR:
Q3-Q1: the middle
50% of the data
•
Sample variance, s
2
:
•
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
•
If the data is skewed or has outliers, the sample
median and IQR are more commonly used.
•
Outliers affect the mean more than the median.
•
Right skewed: mode<median<mean
•
Left skewed: mean<median<mode
•
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.
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- Spring '10
- idontremember
- Normal Distribution, Probability, Variance, Probability theory, discrete random variable, experimenter Control group
-
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