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Collection of Data

Collection of Data. Jim Bohan Manheim Township School District Lancaster PA jim_bohan@mail.mtwp.k12.pa.us. Three Types of Studies. 1. Survey A study in which the researcher gathers data by asking for responses from subjects. 2. Observational Study

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Collection of Data

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  1. Collection of Data Jim Bohan Manheim Township School District Lancaster PA jim_bohan@mail.mtwp.k12.pa.us

  2. 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.

  3. 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.

  4. 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 Bias Bias is a systematic effect that skews all of the data values in a sample.

  5. Types of Sampling: INVALID • Convenience Sampling Choosing the subjects in the sample by convenience. • Voluntary Response Sampling Subjects are included in the sample on the basis of their volunteering to be included.

  6. Valid Types of Sampling: SIMPLE RANDOM SAMPLE

  7. Valid Types of Sampling: STRATIFIED RANDOM SAMPLE

  8. Valid Types of Sampling: SYSTEMATIC SAMPLE

  9. Valid Types of Sampling: CLUSTER SAMPLE

  10. Valid Types of Sampling: TWO STAGE SAMPLE

  11. The Key to VALID SAMPLING Subjects are chosen by the application of a probability rule; that is, based on RANDOM SELECTION

  12. 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.

  13. 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).

  14. 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.

  15. Three Requirements of Controlled Experiments • Comparison • Randomization • Replication

  16. 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.

  17. 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.

  18. Basic Experimental Designs • Completely Randomized Design • Randomized Block Design

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