Statistics 3502/6304Prof. Eric A. Suess

Chapter 2

Collecting Data

• Observational Studies• Surveys• Experimental Studies• Skip section 2.5 for now. This is what is presented in Stat 3503/6305.

The topic is Designs of Experimental Studies.

Part I: Observational Studies

• What is an observational study?• What is an experimental study?

Variables

• What is a variable?• What is an explanatory variable?• What is a response variable?• What is a confounding variable?

The results of a Study

• The goal usually is to make a cause-and-effect conclusion.• This is not usually possible. • With observational studies can show associations, but not causation.• Causation is something discussed with Experimental Studies.• See page 20.

Types of Observational Studies

• Sample Surveys• Prospective Studies• Retrospective Studies• Cohort Studies• Case-Control Studies

Part 2: Surveys

• Target population• Sample• Sampled population• Observational unit• Sampling Unit• Sampling Frame

Example of a survey

• Political Poll• What is the target population? All adults in the US or registered

voters?• What is the sample? A 1000 adults in the US or 1000 people we can

call on landline phones.• The sampled population is very different from the target population.• The observational unit is the phone number.• The sampling unit is the oldest adult, maybe.

Surveys, ways of taking sample

• Simple Random Sample• Stratified Random Sample• Cluster Sample• Systematic Sample

Problems with Surveys

• Nonresponse• Measurement Errors

• Bias

Survey Techniques

• Personal Interviews• Telephone Interviews• Self-Administered Questionaire• Direct Observation

Part 3: Experimental Studies

• Designed Experiments• Factors• Measurements• Observations• Controlled Treatment• Experimental Unit• Measurement Unit• Replication

Examples of an experiment

• Example 2.4 page 32 shrimp farming• Example 2.5 page 34 frying pans• Example 2.6 rats• Example 2.7 shrimp