University of Waterloo Procedures used to Assign Participants to Conditions Essay

I’m working on a psychology multi-part question and need an explanation and answer to help me learn.

reading a research article to understand the purpose and implications of key elements of a study’s methodology,

identifying a research hypothesis and recognizing the IV and DV in an actual study,

• recognizing the procedures used to assign participants to conditions,
• understanding and correctly summarizing the procedures used to manipulate the IV,
• understanding and correctly summarizing the measures used to operationalize the DV, and
• evaluating the internal validity of the methods in an actual study, such as identifying potential procedural confounds.
• Langer, E. J., & Rodin, J. (1976). The effects of choice and enhanced personal responsibility for the aged: A field experiment in an institutional setting. 
• Journal of Personality and Social Psychology, 34(2), 191-198. doi:10.1037/0022-3514.34.2.191