Methods of Randomization

Randomization is a vital part of any research study that utilizes human subjects for research participants; however, while the importance of randomization is universal there are different methods that can be utilized by researchers in order to ensure randomization in the selection of participants for the experimental and control groups.

The most common form of randomization is simple randomization which is based on a single sequence of random assignments that cause participants to be assigned to a group completely at random (Suresh, 2011). An example of this method would be a coin toss being conducted for each participant; the researcher would flip the coin and heads would determine the experimental group while tails would determine the control group. The downside of this method is the complete randomness does not ensure that both groups are made up of an equal number of participants. This method could also be used with rolling dice with the even numbers being the experimental group and the odd numbers being the control group; a deck of cards could also be used with the color corresponding to the group the participant would be placed in.

The second method of randomization is the block randomization method which works by randomizing participants within set blocks such as an equal number of participants are assigned to each group (Efird, 2010). This method allows for participants to be split into blocks based on characteristics like age, gender, or demographics; this fact makes this method ideal for studies that require an equal number of genders or ages to be placed in the experimental group and the control group. Unlike simple randomization, this method can be used to ensure an equal number of participants are placed in each group. The way the process works is the researchers split the participants by the defining characteristics into blocks, then an equal number of participants from each block would be placed in each of the groups. The placement from the blocks to the groups could be done by having a hat filled with pieces of paper with a colored dot on them; the color of the dot would mean the participant would be in the control group or the experimental group. There would be an equal number of each dot color in the hat in order to ensure an equal balance between the two groups.

The third method of randomization is the randomization sequence, also known as sequence generation, a method originally created using Stata 9.0 statistical software which was “stratified by center with a 1:1 allocation using random block sizes of 2, 4, and 6"( Kim & Shin, 2014). This method works by using the software which would randomly assign participants to either the experimental group or the control group using a simple randomization procedure. This procedure would randomly assign each participant in the software with either a number one or a number two; the participant would then be placed in the group that corresponded with their number. An important aspect of this method is that the group chosen for each number was selected prior to the use of the software to prevent a researcher from choosing that those assigned a one should be the experimental group based on a participant that was assigned a one by the software. In order to prevent bias, researchers can choose the number for each group based on a coin toss in order to ensure the selection would also be random.

Drawing Conclusions without Randomization

While most research studies should be conducted utilizing a method of randomization in order to prevent bias and to ensure an equal chance to each participant to be placed in each group, certain situations or types of research can make randomization impossible. For instance, randomization is almost always possible in experimental research studies. Researchers can still make valid conclusions even in situations where randomization is not possible. However, if randomization is not possible, researchers will need to be observed and questioned to ensure they are free of bias before they take part in the research study. When possible, the researchers themselves can also be kept blind to the purpose of the study, meaning while the researcher would need to understand what they would be required to do as part of the study, they would be kept blind to the purpose of the study in order to further prevent bias. The conclusions of a research study would be considered to still be valid if the study was conducted without bias, the study itself was recorded in such a way that it would be replicable with comparable results by other psychology professionals, and the APA Code of Ethics was adhered to during the course of the study.

References

Efird J. (2010). Blocked randomization with randomly selected block sizes. International journal of environmental research and public health, 8(1), 15-20.

Kim, J., & Shin, W. (2014). How to do random allocation (randomization). Clinics in orthopedic surgery, 6(1), 103-9.

Rosnow, R. & Rosenthal, R. (2013). Beginning Behavioral Research: a Conceptual Primer (7th ed.). Boston, MA: Pearson.

Suresh K. (2011). An overview of randomization techniques: An unbiased assessment of outcome in clinical research. Journal of human reproductive sciences, 4(1), 8-11.