Final answer:
If random assignment is not possible, researchers use matching to create comparable experimental and control groups, employ statistical techniques like propensity score matching, and consider single-blind or double-blind approaches to reduce bias.
Step-by-step explanation:
If a researcher cannot randomly assign research participants to experimental or control groups, the next best thing to do is to create comparability through a matching process. This involves carefully selecting participants that have similar characteristics and ensuring that both the experimental group and the control group are closely matched on these characteristics. Characteristics such as age, socioeconomic status, education level, and other relevant variables are taken into account.
To further strengthen the studydesign, researchers might use statistical techniques like propensity score matching, where participants are matched based on a composite score reflecting their likelihood of being in one group or the other based on observed variables. This helps to control for potential confounding variables and makes the groups as similar as possible, apart from the independent variable being studied.
In cases where blinding is possible, a single-blind or double-blind approach can be used to reduce bias. This means that the participants, and sometimes the researchers, do not know who is receiving the intervention or who is in the control group, minimizing the impact of expectations on the results.