1 / 14

The Language of Studies

The Language of Studies. Lecture 8 Secs. 3.1 – 3.3 Fri, Sep 10, 2004. Observation vs. Experimentation. Observational study – A study in which the subjects are not manipulated or controlled in any way, but simply observed.

xanthus-chandler
Télécharger la présentation

The Language of Studies

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. The Language of Studies Lecture 8 Secs. 3.1 – 3.3 Fri, Sep 10, 2004

  2. Observation vs. Experimentation • Observational study – A study in which the subjects are not manipulated or controlled in any way, but simply observed. • Designed experiment – A study in which the researchers actively impose some treatment on the subjects and observe the response.

  3. Think About It • Think About It, p. 131. • Example – Charter School Achievement on the 2003 National Assessment of Educational Progress, page ii, 2ndparagraph.

  4. Explanatory and Response Variables • Response variable – The variable that measures the outcome. It is believed to be affected by the explanatory variable. • Explanatory variable – The variable or factor that is thought to explain the observed outcome. It is believed to affect the response variable.

  5. Let’s Do It! • Example 3.1, p. 132 – Explanatory Variable and Response Variable. • Let’s do it! 3.1, p. 134 – Explanatory Variable versus Response Variable. • Let’s do it! 3.2, p. 134 – Food Myths. • Example – Charter School Achievement on the 2003 National Assessment of Educational Progress, pages ii - iii.

  6. Levels and Treatments • The explanatory variable is typically denoted X. • The response variable is typically denoted Y. • Values of the explanatory variable are called levels. • If there is more than one explanatory variable, then combinations of their values are called treatments.

  7. Example • Example – Charter School Achievement on the 2003 National Assessment of Educational Progress, pages ii – iii.

  8. Confound It! • Confounding variable – A variable whose effect cannot be separated from the effect of the explanatory variable. • If a study has one or more confounding variables, then the researchers cannot attribute changes in the response variable to any one explanatory variable. • Normally, the researchers did not properly control for the confounding variable.

  9. Example • Example 3.3, p. 135 – Treating Multiple Sclerosis with Protein. • Let’s Do It! 3.3, p. 136 – Invasive versus noninvasive Cancer Treatments. • Example – Charter School Achievement on the 2003 National Assessment of Educational Progress, page 3, last paragraph.

  10. Confounding Variables Location Not Cen. City Cen. City lower lower Afr.-Amer. Minority Status Non Afr.-Amer. lower higher

  11. Confounding Variables Location Not Cen. City Cen. City lower lower Afr.-Amer. lower Minority Status Non Afr.-Amer. lower higher higher lower higher

  12. Control by Minority Status Minority Status Non Afr.-Amer. Afr.-Amer. lower lower Charter lower School higher higher Public higher

  13. Control by Location Location Not Cen. City Cen. City lower lower Charter lower Type of School higher higher Public higher

  14. Do Explanatory Variables Explain? • A study cannot prove that variations in the explanatory variable really were the cause of variations in the response variable. • The study can only give evidence supporting that belief. • It may be the case that there is a third variable that is affecting both the explanatory and response variables. • It may be conceivable that the “response” variable affected the “explanatory” variable!

More Related