Single Subject Research Designs

1. Single SubjectResearch Designs

2. We can rarely translate with certainty the average benefit reported in randomized clinical trials to a precise assessment of treatment benefit for an individual patient.John SteinerMedical Researcher

3. Purpose of Single Subject Research • Like randomized pretest-posttest control group experiments, single subject designs are intended to provide strong evidence for cause and effect relationships…for individuals rather than groups.

4. Single Subject Designs: Overview • • Involves the manipulation of one variable to observe its effect on another—an experiment. • • Repeated measurement of the dependent variable before, during, and after treatment. • • Not restricted to one (1) subject, but rarely involves more than three (3) subjects. • • Used extensively in clinical settings (e.g., special education and counseling). • • Subjects serve as their own control.

5. Single Subject Design Requirements • • Reliable measurement • - Multiple measures require reliability • • Repeated measurement • - To develop clear patterns of behavior (stability) • • Clear description and control of the conditions • - In order to strengthen internal/external validity • • Baseline and treatment conditions • - Baseline is before treatment and after treatment • • One variable at a time is investigated • - To strengthen causal claims

6. Single Subject Design • • Notation • - A indicates baseline condition (w/o treatment) • - B indicates the treatment condition

7. Single Subject Design • • A B A • - Multiple observations are made during initial baseline timeframe (A); during treatment implementation (B); and during the second baseline timeframe (A). • • A B A B (conclude with second treatment) • Benefit: Leaves subject with treatment. • Limitation: Cannot evaluate the lasting effects of the treatment.

8. A (baseline) B (treatment) A (baseline)

9. Criteria for Evaluating SS Designs • • Reliable measurement of the target behavior. • • Target behavior is defined in operational terms with a clear description of exactly how it is measured. • • Sufficient measurements are made during each time frame to establish stability (at least 4). • • Full descriptions of the procedures, subjects, and settings are provided. • • Use of one (1) standard treatment. • • Control of experimenter and/or observer effects (single observer introduces threat of bias). • • Results should have practical significance.

10. Self-Experimentation(a type of single subject research)

11. Self-Experiments • Refers to a very special case of single-subject research in which the experimenter conducts the experiment on himself. Usually this means that the researcher, experimenter, and subject of the experiment are all the same.

12. Famous Self-Experiments • • In 1929, Werner Forssmann inserted a catheter into the brachial vein of his own forearm, guided it fluoroscopically into his right atrium, and took an X-ray picture of it. In 1956, he was awarded the Nobel Prize in Medicine for this achievement. • • In 1984, Barry Marshall was able to show that the bacterium Helicobacter pylori, not stress and spicy foods, is the cause of most peptic ulcers by drinking a Petri dish containing the culture and studying the effects. In 2005, he was awarded the Nobel Prize in Physiology for his discovery.

13. Knuckle Cracking and Arthritis

14. Quantified Self (lifelogging) • Mobile apps • Sensor technology • Gamification • Data visualization • Big data

15. Ex Post Facto Research(aka Causal-Comparative)

16. Non-Experimental Designs • • Descriptive: Information about the frequency or amount of something. • • Comparative: Descriptions of the differences between groups. • • Correlational: Description of the relationship between or among variables. • • Ex Post Facto: Description about the relationship between something that has occurred and correlated variables controlled through matching to show cause and effect.

17. Ex Post Facto (Latin: “After the Fact”) • • There are some circumstances where it is impractical, unethical, or illegal to conduct an experiment to determine cause and effect. • • How can you present strong evidence of a cause and effect relationship without an experiment? • • A “Reverse Experiment” • – After the fact, subjects are assigned to “experimental” and “control” conditions (sometimes called comparison groups) using a pair-wise matching procedure on independent variables that matter.

19. Example: Smoking and Birth Defects • • What is the effect of smoking a pack of cigarettes each day on the rate of birth defects among pregnant women in the U.S. ages 20-30? • • We cannot require that some pregnant women smoke while denying cigarettes to others. • • But, some women choose to smoke during pregnancy and others don’t. We don’t manipulate the independent variable (smoking), but we can investigate its effects…after the fact.

20. Ex Post Facto Steps in Smoking Study • 1. Identify independent variables that are likely to have an effect on the dependent variable. • – Age, alcohol & drug use, illness (measles/rubella) • 2. Select a representative sample of 1,000 women who have recently given birth. • 3. Split them into two groups based on smoking status and then pair-wise match them on the IVs. (Discard any unmatched subjects.) • 4. Count the number of babies with birth defects in each group.