Physch: Variables & Experimental Design

What is an independent variable?

The factor manipulated or changed by the researcher to observe its effect.

What is a dependent variable?

The factor measured by the researcher to determine if the IV had an effect.

What is Operationalization?

Defining variables so that they can be accurately manipulated, measured, or quantified and replicated.

What are extraneous variables?

It is a variable other than the Independent Variable that might affect the Dependent Variable if not controlled.

What is a confounding variable?

An uncontrolled variable that acts systemically on one level of the I.V. so it can hide or exaggerate differences between levels and therefore “confound” or confuse the results making it difficult to understand the effect of the IV on the DV.

What is control?

Procedures put in place to ensure extraneous variables remain constant across conditions.

What are experimental designs?

It is the way that the experiment puts people in groups.

What are the 3 types of experimental designs?

Independent groups or independent measures, repeated measures, and matched pairs.

What is an independent measure?

It is two separate groups of participants that are used for each condition of the IV.

ex. One group studies in silence and does a memory task and the other group studies with music and then does the same memory task.

What are the advantages of independent measures?

1. Different ppts are used in each level of the I.V. so there are no order effects.

2. Ppts see only one level of the I.V., reducing the effect of demand characteristics.

3. Random allocation to levels of the I.V. can reduce the effects of individual differences.

What are disadvantages of Independent Measures?

1. Participant variables can distort results if there are important individual differences between participants in different levels of the I.V.

2. More ppts are needed than in a repeated measures designs so the study may be less ethical if ppts are harmed and less effective if there is a small sample because ppts are hard to find.

What are repeated measures?

An experimental design in which each participant performs in every level of the IV.

ex. Each ppt learns in silence and with music and does the memory task after each.

What are the advantages of repeated measures?

1. Participant variables are unlikely to distort the effect of the IV, as each ppt does all levels.

2. Counterbalancing reduces order effects.

3. Uses fewer ppts than independent measures or matched pairs so this is good when ppts are hard to find or are at risk.

What are the disadvantages of repeated measures?

1. Order effects could distort the results.

2. As ppts see the experimental task more than once, they have greater exposure to demand characteristics.

What are matched pairs?

Participants are paired based on relevant shared characteristics (e.g., IQ, age), and one from each pair is assigned to each condition.

ex. Here ppts have been matched for age as age might affect memory, we make sure our two groups contain similar ages. In a memory study, we might also match for IQ and so on.

It is like an independent group design but you carefully match members of each group. If you have a 23yr old rugby player in one group you need one in the other group. If you have a female with an IQ of 150 you need another in the other group.

What are the advantages of matched pairs?

1. Ppts see only one level of the I.V, reducing the effect of demand characteristics.

2. Participant variables are less likely to distort the effect of the I.V. than in an independent measures designs as indivindual differences are matched.

3. Different ppts are used in each level of the IV so there are no order effects.

What are the disadvantages of matched pairs?

1. The similarity between pairs is limited by the matched process, so the right matching criteria must be chosen in advance for this to be effective.

2. Availability of matching pairs may be limited, making the sample size small (although some studies conducted on twins use very large numbers of pairs).

What are participant variables?

Individual differences between participants (such as age, personality, and intelligence) that could affect their behavior in a study that would hide or exaggerate differences between levels of the IV.

What are demand characteristics?

Features of the experimental situation which give away the aims. They can cause ppts to try an change their behavior, for example to match their beliefs about what is supposed to happen, which reduces the validity of the study.

What is random allocation?

A way to reduce the effect of confounding variables such as indivindual differences. Participants are put in each level of the IV such that each person has an equal chance of being in any condition.

What is randomization?

A way to overcome order effects in a repeated measures designs. Each participant is allocated to perform in the different levels of the IV in a way that ensures they have an equal chance of participating in the different levels in any order.

What is counterbalancing?

A way to overcome order effects in a repeated measures design. Each possible order of levels of the IV is performed by a different sub group of participants. This can be described as an ABBA, as half of the participants do condition A then condition B, and half do B then A.

What is matched pairs designs?

An experimental designs in which participants are arranged into pairs. Each pair is similar in ways that are important to the study and one member of each pair performs in a different level of the IV.

What is order effects?

Practice and fatigue effects are the consquences of participants in a study more than once, for example in a repeated measures design. They cause changes in performance between conditions that are not due to the IV, so can obscure the effect of the DV.

What is a practice effect?

A situation where participants performance improves because they experience the experimental task more than once, for example due to familiarity or learning the task.

What is the fatigue effects?

A situation where ppts performance declines because they experience the experimental task more than once, eg. due to physical tiredness or boredom with the task.