There are circumstances when researchers need to study a single participant instead of a group to answer a research question. This type of study is called single-subject, single-case, or single-system design. Such studies often aim at answering the question if an intervention had a significant effect on a dependent variable. However, there are three purposes of single-subject studies, including research, practice evaluation, and monitoring. There are several aspects that need to be considered to conduct a valid study based on one participant.
Valid single-subject research should include at least three features, including repeated measurement, baseline phase, and treatment phase (Check& Schutt, 2012). The dependent variable should be measured several times at an identified interval of time. These measurements should take place before the intervention, or the baseline phase, and during the intervention, or the treatment phase. The dependent variable needs to be measured several times at every stage, to avoid error and improve the reliability of measurements (Check& Schutt, 2012). After the measurements are taken, the data needs to be analyzed to identify if the intervention had a significant effect on the status of the subject.
There are several issues the researchers need to address to ensure that the results of the research are reliable and valid. First, they need to ensure that the measurements are taken properly using standardized instruments and rapid assessment tools (Check& Schutt, 2012). The person who collects the data or the method used to collect the data may have a significant effect on the accuracy of measurements, and researchers need to control for these factors (Check& Schutt, 2012). Second, the researchers need to utilize appropriate data analysis methods to understand if the intervention was effective. There are two general types of analysis: visual analysis of graphed data and utilization of statistical methods, such as chi-square analysis, ANOVA, and t-tests (Check& Schutt, 2012). Visual analysis is commonly used when the differences are evident, while statistics are utilized for subtle differences between the statuses of the subject in the baseline and the treatment phases. Finally, the researchers need to consider possible ethical issues that may arise during the research process (Check& Schutt, 2012). For instance, the researchers need to decide if it is ethical to delay treatment for measuring the independent variable in the baseline phase. Additionally, the researchers need to understand all the factors that may affect the subject, including their families, gender, age, and cultural background.
In summary, single-subject studies can be very useful, especially for clinically-based disciplines, as they can be scientifically credible and clinically relevant (Check& Schutt, 2012). However, researchers need to be skillful in data collection and analysis for single-subject studies, as the procedures differ considerably from studies with multiple participants. Additionally, special attention should be dedicated to ethical issues.
Check, J., & Schutt, R. (2012) Research methods in education. SAGE Publications, Inc.