Importance of Randomization
Randomization is important in psychology experiments for various reasons. For example, it prevents selection and accidental bias (Kang et al., 2008). Participants in research groups should not differ systematically since it would amount to bias, and randomization addresses this issue by arbitrarily allocating subjects to groups. Randomization is also vital since it is important in producing comparable groups and eliminating source bias when assigning treatments (Sourial et al., 2018). Specifically, randomization ensures that researchers and participants or other parties do not have priori knowledge of group assignment, helping achieve allocation concealment. This scenario eliminates selection bias, avoiding unreliable data collection. Further, randomization allows researchers to use probability theory in expressing the likelihood of chance as a contributor to the difference in end outcomes (Lim & In, 2019). After all, randomization ensures that each participant has an equal opportunity to receive any available treatments under study.
Methods of Randomization
The simple randomization method is the most basic and maintains randomness of the assignment of subjects to a particular group. For example, a coin might be tossed for each participant, with the head or tail being assigned to the control or treatment group. Another method is block randomization which seeks to balance sample size across groups over time (Sella et al., 2021). Researchers might also use stratified randomization, which focuses on controlling and balancing the influence of covariates or baseline characteristics when assigning participants to groups (Kang et al., 2008). A researcher creates a block for each combination of covariates and then applies simple randomization to each block to assign subjects to groups. Researchers might also use covariate adaptive randomization, which considers the specific covariates and previous participant assignments to ensure a new participant is sequentially assigned to a particular treatment group (Lim & In, 2019).
Drawing Conclusions Without Randomization
Randomization might not work in all situations since it is not universally feasible or ethical, meaning researchers need alternatives to draw conclusions. Approaches to drawing conclusions without randomization include carefully controlling and measuring potential confounding variables and employing statistical techniques for data analysis (Marcus et al., 2013). For example, researchers can match subjects based on baseline characteristics across different conditions to achieve comparable groups, reducing the effect of compounding variables.
Further, statistical control approaches might help draw conclusions by adjusting for confounding variables through techniques such as analysis of covariance (Dogra & Srivastava, 2012). At the same time, quasi-experimental designs might be used to draw conclusions by comparing naturally occurring groups. Researchers might also use observational studies to observe and measure variables without manipulating them to reach conclusions about variables of interest. Even though these approaches do not establish causal relationships, they can provide meaningful correlational information.
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Sella, F., Raz, G., & Cohen Kadosh, R. (2021). When randomization is not good enough: Matching groups in intervention studies. Psychonomic Bulletin & Review, 28(6), 2085-2093. https://doi.org/10.3758/s13423-021-01970-5
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