Designs of Experiments
Observational Study – observation
and measurement of specific
characteristics – we don’t try to
modify the subjects studied.
Experiment – we apply some
treatment, then observe the effects.
Experimental subjects – subjects in
an experiment.
Cross Sectional Study – data are
observed, measured, and collected at
one point in time.
Retrospective Study – data is
collected from the past by going back
into time.
Propsective study – data is collected
in the future from groups sharing
common factors.
Confounding – is when you cannot
distinguish among the effects of
different factors.
Random sample – each member of a
population has an equal opportunity
of being chosen.
Simple random sample – each
member of a sample has equal
opportunity of being chosen.
Probability sample – members of a
population will know the chances of
being chosen.
Systematic sampling – we select the
nth element in a population – like the
50th person.
Convenience sampling – we use
results that are easy to get.
Stratified Sampling – the population is
subdivided into at least 2 sub-groups.
Then each sub-group is divided again
creating another sub-group within a
sub-group (stratified)
Cluster sampling – divide the
population into sections (clusters) then
randomly choose from the clusters and
use all those chosen randomly.
Sampling error – the difference
between the sample result and the
true population.
Nonsampling error – when sample
data is incorrectly collected