Experimental Methods
1) Laboratory Experiments

A laboratory experiment is a controlled situation in which the researcher manipulates one variable
to measure its effect on another.
Task 1: Decide whether the following points are strengths/weaknesses of laboratory experiments and
write the answers in your exercise books…
2) Field Experiments

Take place outside a laboratory, in a natural setting. However, the basic scientific procedures are still
followed:
 The Independent Variable is manipulated;
 To measure the effect on the Dependent variable.

However, they don’t have to be in a field – in fact they could even be underground!
Task 2: Example 1 - The Subway Samaritan
The researchers arranged for a passenger to fall over on the New
York subway, travelling on a long section – more than 7 minutes.
Aim: The aim was to investigate which factors led people to help
someone in difficulty.
Method: The passengers who witnessed this event were really the
participants, they just didn’t realise it. Students sitting among them would be the observers.
Results: If the man who fell over was holding a walking stick he got helped 95% of the time; If he was
holding a bottle of whisky less people tried to help – only 50% of the time; Women were much less likely
to help the person with the whiskey; The person with whiskey was much more likely to get help from his
own ethnic group.
(Task 2) Answer the follow questions, in your exercise books (Title: The Subway Samaritan).
1. Was there an independent variable being manipulated? If so, what is it?
2. What was the dependent variable?
3. What Experimental Design was used - Independent Measures, Repeated Measures or Matched Pairs?
Task 3: Use the following key terms to evaluate field studies:
 Ecological validity
 Participant reactivity
 Extraneous variables
 Time
 Deception
Are the above bullet points potential strengths or weaknesses of field studies.
3) Natural Experiments
In a natural experiment the researcher makes use of naturally occurring variables. These are not true
experiments because the scientist cannot really manipulate the IV. Sometimes referred to as a “QuasiExperiment”.
Task 4: Example 2 - The Winter War




In 1939 Finland was invaded by Russia.
The Finns fought with immense courage but were eventually
over-run.
Psychologists later found that women who had been pregnant
when their husbands were killed were more likely to have babies
who grew up to be schizophrenic.
It has been suggested that stress on the mother in the middle
stage of pregnancy may cause schizophrenia.
Answer the follow questions, in your exercise books (Title: The Winter War).
1. What was the I.V. in the Winter War ‘experiment’:
2. How did the psychologists manipulate the independent variable?
Advantages
 Allows you to research with groups like drug users, alcoholics, victims of abuse, without creating situations
which are harmful to the participants.
 High level of ecological validity.
Disadvantages
 High level of extraneous variables;
 Difficult to replicate.
Task 5: The columns have been mixed-up.
Match up the type of Experimental Method with each of
the key features…
Experimental Method
Features of
Experiment
LABORATORY EXPERIMENT
An experiment performed in the
natural environment, however the
experimenter still controls the IV.
Weaknesses
Strengths
High degree of control. (All variables
can be controlled in the situation).
Replication of procedures is easy.
The relationship between the IV and
the DV should be easy to determine
as long as the experiment is well
designed.
FIELD EXPERIMENT
Researcher controls
variables as possible.
as
NATURAL EXPERIMENT
many
The researcher makes use of
naturally occurring differences in
the IV. A type of quasi experiment.
Usually conducted in a lab, using
standardised procedures but can be
done anywhere as long as it’s a
controlled environment.
High ecological validity. (Due to
natural settings, results are more
likely to show true behaviour and
results can be generalised to other
situations).
High ecological validity. (Due to
natural settings, results are more
likely to show true behaviour and
results can be generalised to other
situations).
Reduced demand characteristics.
No/reduced demand characteristics.
Less control over IV, DV and
confounding/extraneous variables.
Lack of direct/any intervention by
experimenter.
Less control over IV, DV and
confounding/ extraneous variables.
Replication is difficult as conditions
are unlikely to be exactly the same
again.
Replication is difficult as conditions
are unlikely to be exactly the same
again.
Sample bias- Participants aren’t
randomly allocated to groups.
Sample bias- Participants aren’t
randomly allocated to groups.
Low ecological validity - due to high
levels of control, the situation can
be v. artificial and may not represent
real life.
Experimenter bias.
Demand characteristics.
Variable
Likelihood of the desired behaviour
being displayed can be very rare.
IV occurs naturally.
Measure DV.
Manipulation of IV.
Measure DV.
Manipulation of IV.
Measure DV.
Task 6: Applying Experimental Methods
For each of the following research questions, consider which Experimental Method you would use (lab,
field, or natural experiment) and why? Furthermore, consider which Experimental Design you would
use (Independent Measures, Matched Pairs or Repeated Measures) and why?
 You wish to study how changes in lighting, heating and breaks affect the productivity of workers.

You wish to study how parents in Essex bring up their children.

You wish to study how aggressive behaviour on television affects the behaviour of viewers.

You wish to study how girls in Essex behave towards someone when they have a romantic interest
in them.

You wish to study at what age babies can recognise a human face.

You wish to study whether some teachers are better than others.

You wish to study whether people really get better as a result of psychotherapy sessions.

You wish to study whether there are measurable differences in the personalities of men and
women.
Plenary
RANK THEM
WRITE down 5 things that you have learnt about the topic (Research Methods) so far. Which is the
most important, TELL ME WHY…What is least?
Least
Most
Task 7: Homework
Your task is to answer the following five questions, in relation to the four scenarios below, in your pink
exercise books. Due: Next RM lesson.
1. Identify the IV and DV;
2. Write a Directional and Non-Directional Hypothesis
3. Which Experimental Method (Lab, Field, Natural or Case Study) would you use? Justify your choice.
4. What Experimental Design (independent groups, repeated measures, matched pairs) would you use?
Justify your choice.
A. An experimenter wants to see if drug X improves sport performance. One group are given the
drug, another are given a placebo. Both groups are tested for athletic ability.
B. A researcher is interested in whether alcohol has an effect on memory. One group of participants
are given a list of words to learn and then given an alcoholic drink. The other group is given the
same list of words, and a glass of water. The number of words they can remember is recorded.
C. A psychologist is investigating the effect of music on concentration. A group of participants are
given a series of crossword puzzles to solve, first in a silent room, then when classical music is
played, and then when rock music is played. The time taken to solve each puzzle is recorded.
D. A scientist has developed a drug which he believes will increase IQ. He has two groups of
participants; one group he gives the drug to, and the other he gives a placebo to. After two weeks,
he tests their IQ. To try and avoid any participant variables, he ensures that he has an equal
number of men and women in each group, and that the participants are of similar ages,
intelligence and social background.
Experimental Method
Features of
Experiment
LABORATORY EXPERIMENT
An experiment performed in the
natural environment, however the
experimenter still controls the IV.
Weaknesses
Strengths
High degree of control. (All variables
can be controlled in the situation).
Replication of procedures is easy.
The relationship between the IV and
the DV should be easy to determine
as long as the experiment is well
designed.
FIELD EXPERIMENT
Researcher controls
variables as possible.
as
NATURAL EXPERIMENT
many
The researcher makes use of
naturally occurring differences in
the IV. A type of quasi experiment.
Usually conducted in a lab, using
standardised procedures but can be
done anywhere as long as it’s a
controlled environment.
High ecological validity. (Due to
natural settings, results are more
likely to show true behaviour and
results can be generalised to other
situations).
High ecological validity. (Due to
natural settings, results are more
likely to show true behaviour and
results can be generalised to other
situations).
Reduced demand characteristics.
No/reduced demand characteristics.
Less control over IV, DV and
confounding/extraneous variables.
Lack of direct/any intervention by
experimenter.
Less control over IV, DV and
confounding/ extraneous variables.
Replication is difficult as conditions
are unlikely to be exactly the same
again.
Replication is difficult as conditions
are unlikely to be exactly the same
again.
Sample bias- Participants aren’t
randomly allocated to groups.
Sample bias- Participants aren’t
randomly allocated to groups.
Low ecological validity - due to high
levels of control, the situation can
be v. artificial and may not represent
real life.
Experimenter bias.
Demand characteristics.
Variable
Likelihood of the desired behaviour
being displayed can be very rare.
IV occurs naturally.
Measure DV.
Manipulation of IV.
Measure DV.
Manipulation of IV.
Measure DV.