# UK STA 291 - Categorical/Qualitative (29 pages)

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## Categorical/Qualitative

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## Categorical/Qualitative

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Pages:
29
School:
University of Kentucky
Course:
Sta 291 - Statistical Methods
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Unformatted text preview:

STA 291 Lecture 3 Data type Categorical Qualitative and Quantitative Numerical within categorical nominal and ordinal within quantitative discrete and continuous STA 291 Lecture 3 1 How data are collected experiments and surveys polls Example of experiment clinical trials testing the effectiveness of a new drug Example of survey opinion polls STA 291 Lecture 3 2 In both methods a key ingredient is randomness randomly select people to interview in survey randomly divide patients into two groups in experiment Observational Study Survey STA 291 Lecture 3 3 Methods of Collecting Data I Observational Study An observational study observes individuals and measures variables of interest but does not attempt to influence the responses The purpose of an observational study is to describe compare groups or situations Example Select a sample of men and women age 18 and over and ask whether he she smoke cigarette STA 291 Lecture 3 4 Methods of Collecting Data II Experiment An experiment deliberately imposes some treatment on individuals in order to observe their responses The purpose of an experiment is to study whether the treatment causes a change in the response Example Volunteers divided randomly into two groups One group would take aspirin daily the other would not After 3 years determine for each group the proportion of people who had suffered a heart attack This is an actual study STA 291 Lecture 3 5 Methods of Collecting Data Observational Study Experiment Observational Studies are passive data collection We observe record or measure but don t interfere Experiments are active data production Experiments actively intervene by imposing some treatment in order to see what happens Experiments can tell what caused the change if any STA 291 Lecture 3 6 Why random To eliminate bias STA 291 Lecture 3 7 Collecting data for a poll Simple Random Sampling Each possible sample has the same probability of being selected The sample size is usually denoted by n STA 291 Lecture 3 8

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