Lecture 3 - Experimental Design I

Question 1

What is an independent variable?

Answer 1

• This is a variable which the experimenter systematically varies or manipulates
• Should have at least 2 levels (for comparison)
• Often referred to as the IV

Question 2

What is a dependent variable?

Answer 2

• This is an outcome or measurement variable and is the variable upon which the experimenter is interested in observing effects
• Often referred to as the DV

Question 3

What are the key features of experimental method?

Answer 3

1. Manipulating the Independent Variable (IV)
2. Controlling extraneous variables
3. Measuring the Dependent Variable (DV)

Question 4

What are the different types of independent variables?

Answer 4

• Situational
• Task variables
• Instructional variables

Question 5

What are control groups/ conditions?

Answer 5

Absence of a manipulation

Question 6

What is an experimental group/ condition?

Answer 6

Manipulation is administered

Question 7

What is a random assignment?

Answer 7

Involves non-systematic assignment of participants to conditions

Question 8

What is a manipulation check?

Answer 8

The purpose of this is to ensure that the manipulation has had the desired effect.

Question 9

What are extraneous variables?

Answer 9

• Any variable that is not of immediate interest to a researcher but which may pose a threat to validity because it compromises the interpretation of research findings. This is usually because it obscures the measurement of the processes of interest.
• It generates ‘noise’ in our data

Question 10

What is a confounding variable?

Answer 10

• Unintended or accidental manipulation of an extraneous variable that occurs because that variable (a ‘confound’) is associated with an independent variable (IV) in an experiment.
• Its effect on the DV might be mistaken for the effect of the IV

Question 11

What is a ceiling effect?

Answer 11

E.g., If task is too easy, all scores will be very high. Differences between Ps will be disguised.

Question 12

What is a floor effect?

Answer 12

E.g., If task too difficult, all scores very low. Differences between Ps will be disguised

Question 13

What is the solution to ceiling and floor effects?

Answer 13

• Identify task of moderate difficulty, determined through pilot testing

Question 14

What is a quasi-experimental design?

Answer 14

Differences on IV exist already, they are not manipulated by a researcher