1. Types of Experiments
Lab
Field
Natural
Quasi

2. What is important?
Whether the IV is directly manipulated by the researcher
Where the DV is measured

3. Research question Does drinking coffee improve concentration?
First operationalise!
IV?
DV?

4. Laboratory experiments
Take place in HIGHLY CONTROLLED ENVIRONMENTS.
Doesn’t necessarily have to be a ‘laboratory’, just has to be highly controlled.
Researcher manipulates the IV and records the effect on the DV.

5. Field experiments Takes place in a natural, more everyday setting.
Not literally in a field, in the field.
Researcher manipulates the IV and records the effect on the DV.

6. Natural experiments
The researcher takes advantage of a pre-existing independent variable.
The IV is not brought about by the researcher; it would have happened even if the researcher was not there.

7. Quasi experiments Almost an experiment but not quite!
The IV is based on an existing difference between people (e.g. age or gender).
No-one manipulates the IV, it just exists.

8. STRENGTHS AND LIMITATIONS
Using your textbook, try to add to your table 2 strengths and 2 limitations of each type of experiment.
Highlight words/phrases that you are unsure of, e.g. ‘validity’, ‘reliability’, ‘demand characteristics’ etc.
STRENGTHS
LIMITATIONS
LAB EXPERIMENT
FIELD EXPERIMENT
NATURAL EXPERIMENT
QUASI EXPERIMENT

9. Lab experiments - Evaluation (strengths and Limitations)
+ High control over EXTRANEOUS VARIABLES (researcher can ensure that the change in IV caused the effect on the DV). Therefore, the study demonstrates cause and effect (high INTERNAL VALIDITY).
+ Replication is more possible than in other types of experiment because of the high level of control (ensures new EXTRANEOUS VARIABLES are not introduced when repeating an experiment). This is important to check that the results are VALID and not just a one-off.
- May lack GENERALISABILITY because the lab environment may be artificial and not like everyday life (participants might behave in unusual ways). This means their behaviour can’t be generalised beyond the research setting (low EXTERNAL VALIDITY)
- Participants are usually aware they are being tested in a lab so they might behave unnaturally (DEMAND CHARACTERISTICS).
- The tasks participants carry out in a lab might not represent real-life experience (low MUNDANE REALISM)

10. Field experiments – evaluation (strengths and limitations)
+ Have higher MUNDANE REALISM than lab experiments because the environment is more natural. Therefore, field experiments might produce behaviour that is more VALID and authentic. Especially as participants might not know they are being studied (high EXTERNAL VALIDITY)
- Field experiments have less control over EXTRANEOUS VARIABLES. This means cause and effect between the IV and DV is much harder to establish and REPLICATION is often not possible.
- There are also ETHICAL ISSUES. If participants do not know they are being studied, they cannot give their CONSENT and so the research might invade their PRIVACY.

11. Natural experiments – evaluation (strengths and limitations)
+ Allows research to take place that might not be ethical otherwise.
+ Natural experiments often have high EXTERNAL VALIDITY because they involve the study of real-life issues and problems as they happen.
- A naturally occurring event might happen very rarely, reducing the opportunities for research. This also means that there is less scope for GENERALISING findings to other situations.
- Participants might not be RANDOMLY ALLOCATED to EXPERIMENTAL CONDITIONS, which means the researcher might be less sure that the IV affects the DV.

12. Quasi experiments – evaluation (strengths and limitations)
+ Quasi experiments are often carried out under controlled conditions and therefore share the same strengths as a lab experiment.
- Quasi experiments, like natural experiments, cannot RANDOMLY ALLOCATE participants to EXPERIMENTAL CONDITIONS, and therefore there might be CONFOUNDING VARIABLES.

13. APPLY YOUR KNOWLEDGE…
FOR THE FOLLOWING SCENARIO, DECIDE WHETHER IT IS A LAB, FIELD, NATURAL OR QUASI EXPERIMENT (BE PREPARED TO JUSTIFY YOUR DECISION!):
Baron-Cohen et al (1986) – Got children with Down’s Syndrome, children with Autism and ‘normal’ children to arrange comic strip stories in to the correct sequence. It was found that the children with Autism performed significantly worse when it came to ordering the comic strip.
QUASI EXPERIMENT

14. APPLY YOUR KNOWLEDGE…
FOR THE FOLLOWING SCENARIO, DECIDE WHETHER IT IS A LAB, FIELD, NATURAL OR QUASI EXPERIMENT (BE PREPARED TO JUSTIFY YOUR DECISION!):
Piliavin et al (1969) – Conducted an experiment on a busy New York subway in which a researcher pretended to collapse. It was found that more people helped when the victim was carrying a walking stick than when they smelt of alcohol.
FIELD EXPERIMENT

15. APPLY YOUR KNOWLEDGE…
FOR THE FOLLOWING SCENARIO, DECIDE WHETHER IT IS A LAB, FIELD, NATURAL OR QUASI EXPERIMENT (BE PREPARED TO JUSTIFY YOUR DECISION!):
Williams (1986) – Monitored the change in behaviour of year old children in a Canadian town before and after television was introduced for the first time. Significant increases in levels of aggression were observed after the children had access to television.
NATURAL EXPERIMENT

16. APPLY YOUR KNOWLEDGE…
FOR THE FOLLOWING SCENARIO, DECIDE WHETHER IT IS A LAB, FIELD, NATURAL OR QUASI EXPERIMENT (BE PREPARED TO JUSTIFY YOUR DECISION!):
Gilchrist & Nesburg (1952) – Deprived patients of food and water for 4 hours and showed them pictures of food. These participants rated the pictures of food as being brighter than the control group who had not been food deprived.
LAB EXPERIMENT

17. PREP
Add all the key terms/definitions from today’s lesson that are new to you in your glossary.