Basics of Experimental Design

Question 1

Define a fact.

Answer 1

a statement about a direct observation of nature that is so consistently repeated that virtually no doubt exists as to its truth value.

Question 2

Define Theory.

Answer 2

a collection of statements (propositions, hypotheses) that together attempt to explain a set of observed phenomena.

Makes general predictions upon which specific hypotheses can be based.

Question 3

Define Hypothesis

Answer 3

A clear but tentative explanation for an observed phenomenon.

Question 4

What must a hypothesis be?

Answer 4

• Falsifiable
• Testable
• Precisely stated
• Rational
• Parsimonious (explanation simple as possible)

Question 5

What is a Construct?

Answer 5

• Defined by theoretical definitions.
• Building blocks of theories
• Theoretical concepts formulated to serve as causal or descriptive explanations for a phenomena

Question 6

What is a Variable?

Answer 6

• Must be operational (They are defined explicitly so that they can be measured and expressed quantitatively or qualitatively)
• Any characteristic that can assume multiple values (i.e. can vary)

Question 7

Name the scales of measurement from lowest level to the highest.

Answer 7

• Nominal - named variables
  ○ Numbers assigned serve as labels but don’t indicated numerical relationship
• Ordinal - Named & ordered/ranked
  variables (unequal intervals between ranks)
• Interval - Named, ordered, equal increments, but no real 0 point.
• Ratio - real 0 point, Equal intervals

Question 8

Define independent variables.

Answer 8

Variable that is manipulated and is hypothesised to bring about a change in the variable of interest

Independent variables each have at least 2 levels/conditions

Question 9

Define dependent variables.

Answer 9

The variable that is measured

We compare differences in the DV under the different levels of the IV.

Question 10

What is a between subjects design?

Answer 10

Independent groups

Participants each exposed to one level of the level of the independent variable

Question 11

Issues with between subjects design

Answer 11

Can’t eliminate effects of other variables

But can minimise these effects by spreading their influence across different levels of the IV(s)

Question 12

What is within subjects design?

Answer 12

Repeated measures

Participants exposed to all levels of the independent variable

Question 13

Considerations with within-subject design.

Answer 13

Potentially moderating characteristics are kept equal across the levels of the IV (each participant acts as his/her own control)

requires fewer participants that between subject design.

Question 14

Issues with order effect within ‘within subjects design’.

Answer 14

Order effects - Once participants have been exposed to one level of the IV there’s no way to return them to their original state.

Counterbalancing is used. Order effects will still influence P’s performance, but the effect of that influence will be evenly spread across each level of the IV.

Question 15

What does random allocation do?

Answer 15

• Ensures that each participant is equally likely to be assigned to any IV level
• Distributes the occurrence of potential moderating variables equally among experimental conditions
• Prevents experimenters (un)intentionally biasing their results.
• Enables the use of powerful statistical tests that can help determine causal relationships between variables.

Question 16

What is a Fully Independent Factorial Design (between subjects)?

Answer 16

Each participant takes part in just one experimental condition (1 level of a single IV)

Question 17

What is a Fully Repeated Measures Factorial Design (within subjects)?

Answer 17

Each participant takes part in all experimental conditions (all levels of all IVs)

Question 18

What are Factorial Mixed Designs?

Answer 18

Always contain at least:

• 1 or more within subjects IV(s)
• 1 or more between subjects IV(s)

Each participant takes part in all levels of within subject IV(s) but just one level of between subject IV(s).

Question 19

Define True Experimental Designs.

Answer 19

experimenter has complete control over the assignment of Ps to experimental conditions

Question 20

Define Quasi-experimental designs

Answer 20

the assignment of Ps to experimental conditions is pre-determined.

Difficult to infer causality, hard to randomly assign Ps to IV levels. (differences between groups other than interested variable)

Question 21

What is matching?

Answer 21

For quasi-experimental between subjects designs, where Ps can’t be randomly assigned to IV levels

Solution: Identify potentially moderating variables and match the groups on this basis

Question 22

What are matched pairs?

Answer 22

Pair individual participants on the basis of variables
○ Compare individuals from same background

It’s usually impossible to perfectly match Ps in this way

Question 23

Issue of Within-Subjects Design without counterbalancing

Answer 23

Occasionally it’s not possible to counterbalance the order Ps are exposed to levels of the IV.
Order participants are exposed to levels of the IV is fixed = serious problem as there are likely to be differences between time 1 and time 2 other than the variable of interest.

Must be cautious about inferring causality

Question 24

When are pre-test post-test control group design used?

Answer 24

For within subjects designs where IV levels can’t be counterbalanced

Question 25

What is pre-test post-test control group design?

Answer 25

• mixed design
• Split Ps into 2 groups and manipulate the IV of interest in one group only (there is a control group)
• Control group allows us to account for any order effects present.