collection of data jim bohan [email protected]
TRANSCRIPT
Three Types of Studies
1. Survey
A study in which the researcher gathers data by asking for responses from subjects.
2. Observational Study
A study in which the researcher observes behaviors of the subjects.
3. Controlled Experiment
A study in which the researcher imposes treatments on the subjects.
Methods of Data Collection
• Census:
Studying ALL subjects of the population of interest.
• Sample:
Studying a proper subset of the subjects from the population of interest.
Issues with Sampling
• The purpose of sampling is to generate a proper subset of the population that is representative of the population.
• The major concern with sampling is
BiasBias is a systematic effect that skews all of the data values in a sample.
Types of Sampling: INVALID
• Convenience SamplingChoosing the subjects in the sample by convenience.
• Voluntary Response SamplingSubjects are included in the sample on the basis of their volunteering to be included.
Valid Types of Sampling: SIMPLE RANDOM SAMPLE
Valid Types of Sampling: STRATIFIED RANDOM SAMPLE
Valid Types of Sampling: SYSTEMATIC SAMPLE
1 2 3 4 1 2
3 4 1 2 3 4
1 2 3 4 1 2
3 4 1 2 3 4
1 2 3 4 1 2
3 4 1 2 3 4
Valid Types of Sampling: CLUSTER SAMPLE
Valid Types of Sampling: TWO STAGE SAMPLE
The Key to VALID SAMPLING
Subjects are chosen by the application of a probability
rule; that is, based on RANDOM SELECTION
Controlled Experiments: Vocabulary
• Experiment:
A study in which the researcher imposes treatment(s) on the subjects.
• Controlled Experiment:
A study in which groups receive different treatments whose effects are compared.
• Units:
The subjects who participate in the study.
Controlled Experiments: More Vocabulary
• Subjects:The term applied to human units.
• Control Group:The group who receives either no treatment or a placebo, a treatment that causes no effect.
• Treatment Group(s):The group(s) who receives the treatment(s).
Controlled Experiments: More Vocabulary
• Explanatory Variable:
The variable to which the researcher assigns values in the study: the independent variable.
• Response Variable:
The variable that measures the effect of the value of the explanatory variable: the dependent variable.
Three Requirements of Controlled Experiments
• Comparison
• Randomization
• Replication
Confounding: The Problem
• Two variables are CONFOUNDED when the effects of the explanatory variable cannot be separated among the treatment groups.
• A LURKING VARIABLE is a variable that is not included in the study but may be effecting the results of the experiment.
Confounding: The Solution
The effects of confounding can be minimized by RANDOMIZATION.
The effects of a lurking variable should be spread uniformly among randomized groups.
Basic Experimental Designs
• Completely Randomized Design
• Randomized Block Design