Final answer:
The most appropriate type of research study to determine if premedication with diphenhydramine is more effective than acetaminophen for preventing aseptic meningitis after IV globulin infusion is a randomized trial, due to its ability to compare interventions effectively and minimize bias.
Step-by-step explanation:
To determine if premedication with diphenhydramine is more effective than acetaminophen in reducing the incidence of aseptic meningitis after intravenous globulin infusion, the most appropriate type of research study would be a randomized trial. This study design is specifically aimed at comparing the effectiveness of interventions. Participants would be randomly assigned to two groups: one receiving diphenhydramine and the other acetaminophen prior to their intravenous globulin infusion. By using randomization, the researcher can minimize bias and increase the likelihood that the two groups are comparable, which helps to ensure that any differences in outcomes can be attributed to the premedication rather than other factors. A randomized trial provides a high level of evidence on the efficacy of treatments and would be well-suited to answer the research question.