Random Assignment Of Participants

The word “random” has a precise meaning in statistics.

Random selection doesn’t just mean you can just randomly pick a few items to make up a sample.

The first 25 balls you draw go into the experimental group. Example of non-random assignment: you have a list of 50 people to assign to control groups and experimental groups.

You use your knowledge and experience to choose 25 people who you think would be better suited to the experimental group (a method called purposive sampling).

When attempting to create a relationship between two variables, it is best to discover which of the variables affects the other.

If by the end of an experiment you have discovered which is the dependent variable and which is the independent variable, you will have created a much more valid study than one which simply finds a connection, as you can then start investigating to what extent the IV affects the DV.You choose every 50th student from a list (a random selection method called systematic sampling) to create a sample of 50 students to study.Example of non random selection: From the same list of 5,000 students, you randomly circle 50 names.This isn’t truly random as your biases (known or unknown) could affect who you circle.For example, you might unknowingly circle boys names over girls, or American-sounding names over foreign-sounding names.Example of random assignment: you have a study group of 50 people and you write their names on equal size balls.You then place the balls into an urn and mix them well (this is a classic ball and urn experiment).Strategies such as flipping a coin, assigning random numbers, rolling dice, and even drawing names out of a hat are commonly used.The goal of a psychology experiment is to determine if changes in one variable lead to changes in another variable.In order to create a true random selection, you need to use one of the tried and testing random selection methods, like simple random sampling.Example of random selection: You are studying test taking behaviors at a college of 5,000 students.