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12 Cards in this Set
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Placebo

fake treatment or no treatment


Observational Study

A study where researchers observe individuals and record info of interest. (sample studies are observational)


Experiment

a study where researchers impose treatments and measure responses of individuals.


Definitions

Population : entire group of individuals about which the researcher wants info
Variable: Characteristic measured in the sample. Sample: part of population that is measured. (missin some definitions here) 

NonProbability Sample

A sample chosen using personal judgement to determine which individuals are in sample or not.Probability of having an individual in sample is not available.(This is bad sampling)
Examples: Convenience Sample Voluntary Response Sample MallIntercept Sample Quota Sample 

Def of nonprobability samples

Convenience : as said
MallInterecept: relevant questions to subjects and for which answers can be generalized. Voluntary Response: subjects respond themselves Quota Sample: interviewers select individuals themselves. 

Probability Sample

sample chosen to use some random device that gives each member a chance of being selected. Probability can be computed.
Examples: SRS, Multistage, stratified. 

SRS Explanation

SRS: every possible SAMPLE has equal chance of selection.
Use computer generated software or random digit table or some valid device. 

Random Digit Table

1. Each digit in table has same probability.
2. Knowledge of one part of table gives no info of other part. STEP #1 Subjects assigned numbers STEP # 2 Select a line from the Table for each member. STEP # 3 All no. larger than Population size are eliminated. STEP # 4 Repeated numbers are deleted STEP # 5 Start from step # 1 until you have desired sample size to investigate 

Stratified Sample

1. Classify individuals into groups (strata)
2. Choose Probability Sample within each stratum 3. Combine samples from strata to form a complete sample. 

MultiStage Sample

For three stage sampling:
#1 probability sample of groups is selected #2 probability of sample of subgroups is taken from each selected group # 3 units are sampled from within each selected subgroup. 

Further study on multistage

1. When you increase stages in multistages you are increasing the number of times you will sample in each group.
2. Diff b/w multistage and stratified sample is that in stratified you would sample from every group. But in multistage you select certain groups and then sample from them. In every stage in multistage we "sample diff things in each stage." 