• WRITTEN BY TRMC
• from https://kpu.pressbooks.pub/psychmethods4e/chapter/single-subject-research-designs/

Note: https://opentextbc.ca/researchmethods/chapter/single-subject-research-designs/ has Key Takeaways that might be helpful throughout this chapter

Every research design has strengths and weaknesses. SSRD allows for specific individualized and detailed analysis for behavior. Cost effectiveness and flexibility are among the main advantages of SSRD. SSRD is seen as a complementary method in addition but not the main means for conducting social science experiments for research in social work which is a limitation. SSRD is better used in clinical social work practice. SSRD is individualized as it is idiosyncratic. For instance, one intervention may apply to one person but not to another person. (written by TRMC)

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 behavior. Specifically, the researcher waits until the participant’s behavior in one condition becomes fairly consistent from observation to observation before changing conditions.  One limitation regarding SSRD is that it only uses a single subject for this design without a proper control for comparison. This allows for the outcome to not be generalizable because the sample group is single and often not large enough to generalize for the public.

Some advocates of group research worry that visual inspection is inadequate for deciding whether and to what extent a treatment has affected a dependent variable. One set of concern revolves around the issue of data analysis. Some advocates of group research worry that visual inspection is inadequate for deciding whether and to what extent a treatment has affected a dependent variable. One specific concern is that visual inspection is not sensitive enough to detect weak effects. A second is that visual inspection can be unreliable, with different researchers reaching different conclusions about the same set of data. A third is that the results of visual inspection—an overall judgment of whether or not a treatment was effective—cannot be clearly and efficiently summarized or compared across studies (unlike the measures of relationship strength typically used in group research).

Threats to internal validity

As discussed in the previous chapter, the various alternative justifications that account for the observed shift are sometimes referred to as threats to internal validity. The common threats to internal validity within experimental design could be history, maturation, selection bias, experimental mortality, testing , instrumentations, or statistical regression.

In single-subject experimental designs, the utilization of repeated baseline measurements enables the researchers to mitigate the influence of threats to internal validity. Specifically, repeated measurement can effectively address threats to internal validity related to maturation, instrumentation, statistical regression, and testing; because the repeated assessment allows for the identification of patterns that indicate potential risks to internal validity, which are likely to manifest in the baseline data. Nevertheless, the most substantial threats to internal validity in single study design is history. Repeated measurements in a baseline phase does not effectively account for the influence of an historical event that ma)y transpire between the final baseline assessment and the initial intervention measurement. 

Depending on the types of SSRD design, threats to internal validity also vary. For instance, repeated measurement in  A-B design can rule out threats to internal validity. On the other hand, B-A design which does not have a baseline, may not be able to control the threats to internal validity. The most meticulous designs account for threats to internal validity, whereas monitoring designs show client outcomes without being able to infer that the intervention played a significant role. Consequently, it is significant to comprehend the distinctions between types of designs when evaluating the results of studies.