Chapter 6 ppt
Chapter 6 ppt
Chapter 6 ppt
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<strong>Chapter</strong> 6<br />
Experiments in the Real World<br />
<strong>Chapter</strong> 6 1
Thought Question 1<br />
Suppose you are interested in determining if drinking a glass<br />
of red wine each day helps prevent heartburn. You recruit<br />
40 adults age 50 and older to participate in an experiment.<br />
You want half of them to drink a glass of red wine each day<br />
and the other half to not do so. You ask them which they<br />
would prefer, and 20 say they would like to drink the red<br />
wine and the other 20 say they would not. You ask each of<br />
them to record how many cases of heartburn they have in<br />
the next six months. At the end of that time period, you<br />
compare the results reported from the two groups. Give<br />
three reasons why this is not a good experiment.<br />
<strong>Chapter</strong> 6 2
Experiments: Some Techniques<br />
Double-blinding<br />
– to control experimenter/respondent bias<br />
Pairing or blocking<br />
– to reduce a source of variability in responses<br />
– the same or similar subjects receive each<br />
treatment<br />
different from a completely randomized design,<br />
where all subjects are allocated at random<br />
among all treatments<br />
<strong>Chapter</strong> 6 3
Double-Blinded:<br />
Case Study<br />
Quitting Smoking with Nicotine Patches<br />
(JAMA, Feb. 23, 1994, pp. 595-600)<br />
Variables:<br />
– Explanatory: Treatment assignment<br />
– Response: Cessation of smoking (yes/no)<br />
Double-blinded<br />
– Participants do not know which patch they<br />
received<br />
– Nor do those measuring smoking behavior<br />
<strong>Chapter</strong> 6 4
Pairing or Blocking:<br />
Case Study<br />
Quitting Smoking with Nicotine Patches<br />
(JAMA, Feb. 23, 1994, pp. 595-600)<br />
Variables:<br />
– Explanatory: Treatment assignment<br />
– Response: Cessation of smoking (yes/no)<br />
Blocking?<br />
– consider men and women separately?<br />
– could use a matched-pairs design<br />
– self-pairing? Not if cessation is the goal<br />
<strong>Chapter</strong> 6 5
Experiments:<br />
Difficulties and Disasters<br />
Extraneous variables<br />
– Confounding variables (in chapter 5)<br />
– Interacting variables<br />
Hawthorne, placebo and experimenter<br />
effects<br />
Refusals, nonadherers, dropouts<br />
Extending the results (generalizing)<br />
<strong>Chapter</strong> 6 6
Interacting Variables<br />
The problem:<br />
– effect of explanatory variable on response variable<br />
may vary over levels of other variables.<br />
The solution:<br />
– measure and study potential interacting variables.<br />
does the relationship between explanatory and response<br />
variables change for different levels of these interacting<br />
variables?<br />
if so, report results for different groups defined by the levels of<br />
the interacting variables.<br />
<strong>Chapter</strong> 6 7
Interacting Variables:<br />
Case Study<br />
Quitting Smoking with Nicotine Patches<br />
(JAMA, Feb. 23, 1994, pp. 595-600)<br />
Researchers considered:<br />
– smoker at home<br />
found this to be an interacting variable:<br />
Percent quitting Nicotine Placebo<br />
Smoker at home 31% 20%<br />
No smoker at home 58% 20%<br />
– other variables: age, weight, depression<br />
no interactions found<br />
<strong>Chapter</strong> 6 8
Hawthorne, Placebo and<br />
The problem:<br />
Experimenter Effects<br />
– people may respond differently when they<br />
know they are part of an experiment.<br />
The solution:<br />
– use placebos, control groups, and doubleblind<br />
studies when possible.<br />
<strong>Chapter</strong> 6 9
Hawthorne, Placebo and<br />
Experimenter Effects :<br />
Case Study I<br />
1920’s Experiment by Hawthorne Works<br />
of the Western Electric Company<br />
What changes in working conditions<br />
improve productivity of workers?<br />
– More lighting?<br />
– Less lighting?<br />
– Other changes?<br />
All changes improved productivity!<br />
Workers behaved differently when they<br />
knew they were part of a study.<br />
<strong>Chapter</strong> 6 10
Hawthorne, Placebo and<br />
Experimenter Effects :<br />
Case Study II<br />
Experimenter Effects in Behavioral Research<br />
(Rosenthal, 1976, Irvington Pub., p. 410)<br />
Teachers given a list of student names<br />
– told these were students “who would show unusual<br />
academic development.”<br />
IQ was measured at end of year<br />
– first graders on list: 15 points higher<br />
– second graders on list: 9.5 points higher<br />
– older: no striking difference<br />
Great expectations = self-fulfilling prophecy<br />
– students were randomly selected (did not have high IQ)<br />
<strong>Chapter</strong> 6 11
Extending the Results<br />
( Can We Generalize? )<br />
The problem:<br />
– lack of generalizability due to:<br />
unrealistic treatments<br />
unnatural settings<br />
sample that is not representative of population<br />
The solution:<br />
– Researchers should use natural settings<br />
with a properly chosen sample.<br />
<strong>Chapter</strong> 6 12
Extending the Results :<br />
Case Study<br />
Does Aspirin Prevent Heart Attacks?<br />
(NEJM, Jan. 28, 1988, pp. 262-264)<br />
Participants were measured in their<br />
natural setting (at home)<br />
Only healthy male physicians were<br />
participants<br />
– Results may not apply to:<br />
male physical laborers<br />
women<br />
<strong>Chapter</strong> 6 13
Key Concepts<br />
Double-Blind Experiment<br />
Difficulties and Disasters<br />
Experimental Designs<br />
– Completely Randomized Design<br />
– Matched Pairs Design<br />
– Block Design<br />
<strong>Chapter</strong> 6 14