Single Subject Design - Research Design

Research Design: single subject design -
History of studying the individual
Single subject research
Features of single subject designs
Reversal designs
Multiple baseline designs
Data analysis in single subject research
Advantages of single subject research
Disadvantages of single subject research

1. Single Subject Design Made by psychologist Stella

2. History of Studying the Individual Psychology, though, actually began with intensive, prolonged study of the individual. This single-participant research strategies followed from the earlier scientific paradigms employed by physiologists. The individual approach of Gustav Fechner in 1860 had earth-shaking consequences for the development of a new science of psychology when he developed our methods of psychophysics and also formalized Weber’s famous law. Ivan Pavlov who studied the long-term conditioning history of his dogs to provide us with our contemporary principles of conditional responses. Wihelm Wundt and other early psychologists studied mental processes under one or more sequential conditions, all within the same person. Hermann Ebbinghaus (1913) early use of single-subject resarch in psychology.

3. Single -Subject research Single-subject research—which involves testing a small number of participants and focusing intensively on the behaviour of each individual—is an important alternative to group research in psychology . Single-subject studies must be distinguished from case studies , in which an individual case is described in detail. Case studies can be useful for generating new research questions, for studying rare phenomena, and for illustrating general principles . However, they cannot substitute for carefully controlled experimental or correlational studies because they are low in internal and external validity. Single-subject research has been around since the beginning of the field of psychology. Today it is most strongly associated with the behavioural theoretical perspective, but it can in principle be used to study behaviour from any perspective .

4. General Features of Single-Subject Designs First, the dependent variable (represented on the y-axis of the graph) is measured repeatedly over time (represented by the x-axis) at regular intervals . Second, the study is divided into distinct phases, and the participant is tested under one condition per phase . The conditions are often designated by capital letters: A, B, C, and so on.  The conditions are often designated by capital letters: A, B, C, and so on. Thus Figure represents a design in which the participant was tested first in one condition (A), then tested in another condition (B), and finally retested in the original condition (A).

5. General Features of Single-Subject Designs Another important aspect of single-subject research is that the change from one condition to the next does not usually occur after a fixed amount of time or number of observations . Instead, it depends on the participant’s behaviour. Specifically, the researcher waits until the participant’s behaviour in one condition becomes fairly consistent from observation to observation before changing conditions . This is sometimes referred to as the steady state strategy ( Sidman , 1960)

6. Reversal Designs The most basic single-subject research design is the reversal design, also called the ABA design . During the first phase, A, a baseline is established for the dependent variable. This is the level of responding before any treatment is introduced, and therefore the baseline phase is a kind of control condition. When steady state responding is reached, phase B begins as the researcher introduces the treatment . There may be a period of adjustment to the treatment during which the behaviour of interest becomes more variable and begins to increase or decrease. Again, the researcher waits until that dependent variable reaches a steady state so that it is clear whether and how much it has changed . Finally, the researcher removes the treatment and again waits until the dependent variable reaches a steady state . This basic reversal design can also be extended with the reintroduction of the treatment (ABAB), another return to baseline (ABABA), and so on.

7. Reversal Designs Figure: ABAB Reversal Design

8. Multiple-Baseline Design Sometimes, a researcher may be interested in addressing several issues for one student or a single issue for several students. In this case, a multiple-baseline design is used. “In a multiple baseline across subjects design, the researcher introduces the intervention to different persons at different times. The significance of this is that if a behavior changes only after the intervention is presented, and this behavior change is seen successively in each subject’s data, the effects can more likely be credited to the intervention itself as opposed to other variables . Multiple-baseline designs do not require the intervention to be withdrawn. Instead, each subject’s own data are compared between intervention and non-intervention behaviors , resulting in each subject acting as his or her own control ( Kazdin , 1982). 

9. Multiple-Baseline Design An added benefit of this design, and all single-case designs, is the immediacy of the data . Instead of waiting until post-intervention to take measures on the behavior , single-case research prescribes continuous data collection and visual monitoring of that data displayed graphically , allowing for immediate instructional decision-making. In a multiple-baseline design, baselines are established for different participants, different dependent variables, or different settings—and the treatment is introduced at a different time on each baseline . If the introduction of the treatment is followed by a change in the dependent variable on each baseline, this provides strong evidence of a treatment effect.

10. Multiple-Baseline Design

11. Data Analysis in Single-Subject Research Single-subject researchers typically analyze their data by graphing them and making judgments about whether the independent variable is affecting the dependent variable based on level, trend, and latency .

12. Advantage of Single-Subject Research Group means could conceal patterns that appear in individuals' data. Big effects - only clinically significant effects are likely to be found. Ethical and practical advantages ( eg ; can not withhold treatment; too few subjects). Flexibility.

13. Advantage of Single-Subject Research Those who use the single-subject approach find it both a powerful and satisfying research method. One reason for this is that the method provides feedback quickly to the investigator about the effects of the treatment conditions . The experimenter knows relatively soon whether the treatment is working or not working . Day-to-day changes can be observed first hand, quickly and in individual participants . In contrast to the single-subject approach, a large sample statistical approach may take weeks or months of testing participants, calculating means , then performing statistical analyses, etc., and unfortunately, often nothing may be known about the effects of the treatment conditions until the final statistical analysis is complete

14. Advantage of Single-Subject Research The single-subject method also allows us to draw strong conclusions regarding the factors controlling the dependent variable , yet the method does not use random assignment. The method allows strong conclusions because investigators employing it use procedures that provide rigorous control over environmental-experimental conditions with great emphasis on obtaining stable behavior with each participant. To be an acceptable scientific work, the research must demonstrate for each participant that behavior is controlled by the treatment condition and he or she must also show both intra- and inter-participant replication . That is, control must be shown both within a single participant and also between the participants.

15. Disadvantage of Single-Subject Research Can not examine any between-subject effects. Can not detect small effects. May be less generalizable .

16. Disadvantage of Single-Subject Research One obvious limitation of the single-subject approach is that the method is unsuitable for answering actuarial types of questions . Questions such as, " How many of the one-hundred people exposed to a particular treatment will respond favorably and how many will respond unfavorably ?" A similar question relates to studies comparing two or more different treatments on the same behavioral measure. For example, which of the various treatments is the most effective? Ineffective? Debilitating? The method cannot be used if you are interested in treating an entire group of participants, such as a classroom, in an identical way on a daily basis, i.e., when changes in procedures are made, they are made for everyone in the group at the same time and for the same period. A different method is also required if "after the fact" studies (ex post facto, correlational , passive observational) are of interest.

17. Disadvantage of Single-Subject Research Single-subject approach makes heavy time demands . Establishing a criterion and acquiring stable baselines for the response of interest are sometimes very difficult. Further, determining whether variability in behavior is intrinsic or extrinsic can be troublesome. Non-reversible (irreversible) behavior poses its own set of problems and it precludes the use of a design in which the researcher removes the treatment to observe a return to baseline levels of responding. Failure to obtain intra- and inter-participant replication for whatever reason creates problems for the single subject approach. Sometimes decisions regarding the necessary number of both intra- and inter-participant replications are largely subjective . Nevertheless, in spite of the limitations and problems described here, the single-subject method does provide researchers with another powerful way to assess behavior .

18. Reference http://condor.depaul.edu/dallbrit/extra/psy242/242-single-subject.htm https://knowledgesociety.usal.es/sites/default/files/Single%20Subject%20and%20Time%20Series%20Designs.pdf https://opentextbc.ca/researchmethods/chapter/single-subject-research-designs/

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