A. Collecting Data

1. CONTROLLED EXPERIMENTS: the researcher ASSIGNS a treatment and observes the outcomes.

   Sildenafil handout

   Principles of Experimentation

   • CONTROL FOR (or eliminate) potential confounding factors.
   • ASSIGN some patients to get the new drug and others not.

     a. The best method is RANDOM assignment, to eliminate bias.

     b. Patients getting the new drug form the TREATMENT GROUP; patients not getting the new drug form the CONTROL GROUP.

   • Make the experiment BLIND.

     a. Give the control group a PLACEBO (a do-nothing drug).

     b. Do not let the patients know whether they are getting the new drug or the placebo.

     c. This eliminates the "PLACEBO EFFECT", when patients get better just because they think they are getting a drug.

   • Make the experiment DOUBLE BLIND.

     a. Do not let the doctors examining the patients know which drug the patients are getting.

     b. This eliminates any bias in the doctors' judgements.

     c. Sometimes double blinding is impossible.

   • Once the experiment is concluded, COMPARE the two groups.
   • If possible, REPLICATE the experiment.
   • Don't be afraid.

     Even if a study is not a randomized double-blind controlled experiment, it may not be worthless; it depends on how the study was done and what sources of bias may exist. The upshot of doing all of this is to eliminate all possible forms of contamination.

Experiments need not be limited to medical trials (such as the examples in Chapter 1 of the text). School districts, police departments, transportation companies (e.g. airlines, taxis), just about anyone can conduct experiments.

Experiments are the best way of making comparisons about which we can feel confident, but sometimes they are not feasible or ethical (e.g. imagine setting up a randomized experiment involving the effects of living near nuclear power plants). In many disciplines, observational studies are more commonly found for these reasons.

2. Observational Studies

1. Basic idea: the researcher collects the data as they currently are, he or she is not "in charge" of the situation.
2. Definition

   An OBSERVATIONAL STUDY is an assessment of treatments, policies, or exposures and their associated outcomes.

   Studies on the effects of smoking are always observational. See text p.12-13

   Observational studies differ from experiments in that the researcher has no control over which subjects are assigned the treatment. He or she collects data as they currently are. These studies are common when questions are asked that cannot be easily answered with an experiment (e.g. smoking, dangerous or harmful behaviors).

   Surveys are a typical example of observational studies. For example also see the the most recent Election 2000 Survey for the New Hampshire Primary .

3. Remarks

   a. Observational studies are the most useful for descriptive statements of fact. Surveys/polls are the best examples.

   b. Observational studies are dangerous to use for cause-and-effect conclusions because of CONFOUNDING FACTORS (outside factors which can interfere with outcomes).

   Cannot be certain if it is something about loud music be eliminated by CONTROLLING FOR that factor by dividing the population under study into subgroups based on those factors.

4. Other Examples

   a. According to insurance records, people who drive red cars are more likely to get into accidents than people who drive white cars.

   (This is an oservational study; as a statement of fact, it is true that drivers of red cars are more likely to be in accidents; but painting a person's red car white will not make them a better driver.)

   b. According to medical records, the disease pellagra was associated with flies: where there were flies, there was more likely to be pellagra.

   (Again, this is observational; flies are a useful marker of pellagra; but flies are also an indicator of poverty, and pellagra is a disease of malnutrition, not infection.)

   In the United States, pellagra has often been called the disease of the four D's -- dermatitis, diarrhea, dementia, and death. In 1912, the state of South Carolina alone reported 30,000 cases and a mortality rate of 40 percent. While hardly confined to Southern states, the disease seemed especially rampant there.

   c. According to medical records, smokers are more likely to die of heart attacks than nonsmokers. A possible confounding factor is perhaps gender: men are more likely to smoke, and men are naturally at a higher risk of heart attacks. How can gender be eliminated as a confounding factor?

   (If only men are examined, and male smokers are compared to male nonsmokers, then gender plays no role, since everybody is male.)

   d. (Fisher's "constitutional hypothesis":) Suppose a researcher believes that smoking is confounded by genetics; some people have a gene within them that makes them want to smoke; and whether or not they smoke, the gene causes them to get lung cancer. How can genetics be eliminated as a confounding factor?

   (Compare monozygotic identical twins!)

B. Comparing Experimental and Observational Studies

1. Randomized, controlled experiments are more expensive and more difficult to do than observational studies.
2. Experiments can also be unrealistic (in an artificial setting) and unethical (smoking studies).
3. Controlled Experiments are better than observational studies in that a researcher can begin to eliminate confounding and pin down cause and effect. Here researchers impose a treatment on randomized subjects. This is not true of observational studies.

C. Homework Problems (due 1/21/00)

From Excerise Set A: 12-15 (on pages 23-24)
From Review Exercises: 4, 7, 8 (on pages 24-27)