experimental designs Flashcards
types of experiments
- lab
- field
- quasi
lab experiments
- the IV is manipulated by the researcher and the experiment is carried out in a laboratory or other contrived setting away from the participants’ normal environment
advantages of lab experiments
- Good control of extraneous variables.
- Casual relationships can be determined.
- Strict procedures allow them to be replicated, so researchers can be more confident about their findings.
disadvantages of lab experiments
- The artificial situation could make participants behaviour unrepresentative.
- Participants could respond to demand characteristics and alter their behaviour.
field experiments
- the IV is manipulated by the researcher but this time the experiment is carried out using participants in their normal surroundings
advantages of field experiments
- As participants are in their normal situation, their behaviour is likely to be representative.
- Participants could be unaware they are in a study, so demand characteristics are less problematic than in laboratory experiment.
disadvantages of field experiments
- Control over extraneous variables is more difficult than in a laboratory, so they are less reliable and replication is more difficult.
- The researchers cannot be sure that changes in the DV have been caused by changes in the IV.
- Ethical issues.
quasi experiments
the IV is naturally occurring (e.g. cloudy conditions versus sunny conditions; morning versus afternoon), not manipulated by the researcher
advantages of quasi experiments
- they can be used to study real world issues. - If participants are in their normal situations their behaviour is likely to be representative.
- If participants are unaware they are in a study, demand characteristics will be less problematic. - They enable researchers to investigate variables that could not practically or ethically be manipulated.
disadvantages of quasi experiments
- They are only possible when naturally occurring differences arise.
- Control over extraneous variables if often very difficult.
- As the researcher is not manipulating the IV, they can be less sure of the cause of changes in the DV, e.g. a casual relationship cannot be established.
experimental designs
- repeated measures
- independent measures
- matched groups design
repeated measures design
this involves using the same people in each condition
advantages of repeated measure design
- Individual differences are unlikely to distort the effect of the IV, as the participants do both levels. - Counterbalancing reduces order effects.
- Uses fewer participants so is good when participants are hard to find.
- Blind procedures can reduce demand characteristics.
disadvantages of repeated measures
- Order effects such as practice and fatigue and other extraneous variables could distort the results. - Participants see the experimental task more than once, increasing the risk of demand characteristics.
independent measures design
this involves using different people in each condition
advantages of independent measures design
- Different participants are used in each level of the IV so there are no order effects.
- Participants see the experimental task only once, reducing the risk of demand characteristics.
- Effects of individual differences reduced by random allocation to levels of IV.
disadvantages of independent measure design
- Individual differences could distort results if participants in one level of IV differ from those in another.
- More participants are needed than with repeated measures design, which may be less ethical or harder to find.
matched groups design
involves using different people in each condition but an attempt is made to make the participants as similar as possible on certain key characteristics (any that might influence the findings).
- This is done by testing the individuals on the key characteristics, pairing them based on similar scores, and then placing one member of each pair into each group.
advantages of matched groups design
- Participants see the task once, reducing the risk of demand characteristics.
- No order effects.
-Controls for individual differences.
disadvantages of matched groups design
- Similarities between pairs is limited and may be flawed if important variables for matching are unknown.
- Time consuming and difficult.
type of extraneous variables
- participant variables
- situational variables;
> order effects
> environmental factors
> demand characteristics
participant variables
- examples; Age, intelligence, motivation, skill, experience, gender.
- how they are controlled;
> same people in each condition (repeated measures design) or extremely similar people in each condition (a matched groups design). - If using an independent groups design, allocates participants to conditions on a random basis so that participant variables are more likely to be evenly distributed between conditions.
situational factor - order effects
- examples; If doing the same activity twice, participants may do better the second time because of practice or worse because of boredom.
- how they are controlled;
> Having different people in each condition will avoid this problem, which would be a benefit of using either an independent measures design or a matched pairs design.
> If a repeated measures design is used, then this should be counter-balanced. This is where the participants are split into two groups: group 1 does condition 1 first then condition 2, while group 2 does condition 2 first then condition 1.
situational factor - environmental factors
- examples; such as time of day, temperature and noise
- how they are controlled;
> impose controls on the experiment to ensure that there are as few differences as possible between the two conditions (e.g. do both conditions in the same room, with the same temperature levels, same colour walls, same light levels, etc.).
situational factor - demand characteristics
- examples; these are cues in an experiment that communicate to participants what is expected of them and which may unconsciously affect the behaviour of participants.
- how they are controlled;
> Do not tell participants the aim of the investigation. (This is known as a single blind procedure)
researcher bias
- term used to describe effects of a researcher’s expectations on a participant’s behaviour.
- To control for this, standardised instructions should be used to ensure the experimenter says the same things to each participant and to prevent any hints from being given. If the participant can be left uncertain as to what the precise aim of the research is, this is known as single blind.
