Final answer:
The Two-standard deviation band method is the graphic method commonly used to analyze data in single-subject research studies, as it allows for the examination of data variability and trend changes over time, which are essential in these kinds of research designs.
Step-by-step explanation:
Among the graphic methods commonly used to analyze data in a single-subject research study, the correct option is d. Two-standard deviation band method. This method involves plotting individual data points over time and adding bands that represent two standard deviations above and below the mean. This allows researchers to examine how the data deviate from the mean and to assess the effects of interventions within the scope of the study.
While other graphs like line graphs, pie graphs, and bar graphs are useful in displaying data, they may not specifically suit the needs of single-subject research analysis as well as the two-standard deviation band method. This graphical technique is especially important in single-subject designs because it can illustrate both variability in the data and trend changes over time, which are critical aspects in evaluating the effectiveness of the targeted intervention in these studies.