1. Chapter 13 Principles of Experimental Design

2. Types of Studies  Observational – observe and measure something that is already taking place while trying not to influence or cause change.  Retrospective – past records are reviewed  Prospective – subjects are selected and then observed.  Can only show association not causation

3. Types of Studies  Experimental – researchers impose some change or treatment and measure the result or response.  If done correctly can suggest a causal relationship.

4.  Among a group of disabled women aged 65 and older who were tracked for several years, those who had a vitamin B 12 deficiency were twice as likely to suffer severe depression as those who did not.  Type of study?  What was the parameter of interest?  Conclusions you can draw?

5.  Athletes who had suffered hamstring injuries were randomly assigned to one of two exercise programs. Those who engaged in static stretching returned to sports activity in a mean of 37.4 days (SD = 27.6 days). Those assigned to a program of agility and core stabilization exercises returned to sports in a mean of 22.2 days (SD = 8.3 days).

6. Components of a Study  Experimental unit – the thing that is receiving the change.  Called subjects or participants if dealing with humans.  Factor – the thing the researcher changes (explanatory variable)  Level – specific values that the experimenter chooses for the factor.  Treatment – the different levels of a single factor or combination of levels and factors.

7. Bias in an Experiment  In what ways could there be bias in an experiment?

8. Components of a Study  Response Variable – the variable whose values are measured and compared across different treatments.  Control Group – the experimental units assigned to a baseline treatment level to provide a basis for comparison.  Placebo – A treatment known to have no effect. Administered so that all groups experience the same conditions.

9. Components of a Study  Single-Blind –when all the individuals in either the subjects or experimenters are not aware of how the treatments have been allocated.  Double Blind – when all the individuals in BOTH subjects and experimenters are not aware of how the treatments have been allocated.  Placebo effect – The tendency of many human subjects (~20%) to show a response even when administered a placebo.

10. Example  A consumer group wants to test cake pans to see which works best (bakes evenly). It will test aluminum, glass and silicone pans in both gas and electric ovens.  Identify the following:  Experimental Units  Factors  Levels  Response variables  Treatments.

11. Principles of Experimental Design  Control – eliminating all other sources of variation except the factor we are manipulating.  Randomization – assigning treatments randomly to allow us to equalize the effects of unknown or uncontrollable sources of variation.  Replication – Making sure the experiment is repeatable and the experiment is conducted multiple times.

12. Types of Design  Blocking – grouping of similar individuals together to remove variability due to the difference among the groups so we can see differences caused by the treatments more clearly.  Randomized block design – randomization occurs within each block  Completely randomized design – all subjects have an equal chance of receiving any treatment.

13.  Athletes who had suffered hamstring injuries were randomly assigned to one of two exercise programs. Those who engaged in static stretching returned to sports activity in a mean of 37.4 days (SD = 27.6 days). Those assigned to a program of agility and core stabilization exercises returned to sports in a mean of 22.2 days (SD = 8.3 days).

14.  After menopause many women take supplemental estrogen. There is some concern that if these women also drink alcohol, their estrogen levels will rise too high. Twelve volunteers who were receiving supplemental estrogen were randomly divided into two groups, as were 12 other volunteers not on estrogen. In each case, one group drank an alcoholic beverage and the other a non- alcoholic beverage. An hour later everyone’s estrogen level was checked. Only those on supplemental estrogen who drank alcohol showed a marked increase.