By using assignment of participants to treatment conditions, investigators increase the chances that participants' characteristics will be equally distributed across treatment groups. sequential random systematic correlational

I believe by using random assignment of participants to treatment conditions, investigators increase the chances that participants' characteristics will be equally distributed across treatment groups. Random assignment refers to the use of chance procedures in psychology experiments to ensure that each participant has the same opportunity to be assigned to any given group. Study participants are randomly assigned to different groups, such  as the experimental group, or treatment group. 

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