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, observational study we observe the individuals and measure variables of interest but do not attempt to
influence the responses
experiment deliberately impose some treatment on individuals in order to observe their
responses
voluntary response sampling consists of people who choose themselves by responding to general appeal (these
people could have very strong opinions that is why they are respondinG)
convenience sampling choosing individuals who are easiest to reach (ex. polls taken at shopping malls)
simple random sample simplest way to use chance to select a sample by in essence placing names in a
population and drawing a sample
-every individual has an equal chance to be selected)
probability sample sample is chosen by chance
-no equal opportunity for all
stratified random sample divide the population into groups (strata) and then choose separate SRS in each;
then combine the SRS's to form a sample
cluster sampling divides the population into clusters; some of these clusters are randomly selected;
and THEN individuals are selected in the sample
Principles of Experimental Design 1. Control
2. Replicate - each treatment must have as many units as possible to reduce
chance of variation
3. randomize
placebo effect a dummy treatment - gets rid of biased
control group every experiment needs a control group. and this is the group that receives the
dummy treatment
disjoint events aka mutually exclusive events meaning that they cannot occur simultaneously or at
the same time