Lecture 1 Flashcards
(9 cards)
observational study
In an observational study we observe individuals and measure variables of interest but do not attempt to influence the responses
Randomized Experiment
In an experiment we deliberately impose some treatment on individuals and we observe their responses.
Randomization
The use of chance to divide experimental units into groups is called randomization
Randomization produces two groups of subjects that we expect to be similar in all respects before the treatments are applied.
Randomized Block Design
A block is a group of experimental units or subjects that are known before the experiment to be similar in some way that is expected to affect the response to the treatments. In a block design, the random assignment of units to treatments is carried out separately within each block.
Matched Pairs Design
Matched pairs are a common form of blocking for comparing just two treatments. In some matched pairs designs, each subject receives both treatments in a random order. In others, the subjects are matched in pairs as closely as possible, and one subject in each pair receives each treatment.
Observational Study; Policy Analysis
Note that in policy analysis, if researchers (or the government, or foundations) intervene in the lives of study participants by providing a “treatment” (program), but no randomization is done, the study is still called an observational study
Weakness of Observational Studies
Observational studies of the effect of one variable on another often fail because of confounding between the explanatory variable and one or more lurking variables
Lurking Variable
Lurking Variable: a variable that is not among the explanatory or response variables in a study, but that may influence the response variable
Confounding
Confounding occurs when two variables are associated in such a way that their effects on a response variable cannot be distinguished from each other
