Experimental methods

How science works

EXPERIMENTAL METHODOLOGY
Wednesday 12 February 2014

www.jamiesmind.co.uk

1

Can you test these? How?
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.

You accidentally swallow about 8 spiders a year.
You only use 10% of your brain.
Men think about sex every seven seconds.
There are more people than chickens in the world.
The Great Wall of China is the only human-made
object visible from the moon.
Sneezing seven times in a row is the same as an
orgasm.
If you sneeze with your eyes open your eyes will pop
out of your head.
It is impossible to lick your elbow.
Dogs and cats are colour-blind.
Goldfish only have a 7 second memory.



2

Learning Objectives

By the end of this lesson you:
• Must be able identify and describe the different
types of experimental methodology in
Psychology.
• Should be able to identify the idenpendent and
dependent variables from an experimental aim.



3



4

Types of Experiments
• Laboratory experiments
– Highly controlled / artificial situation
– The experimenter has explicit control over the IV

• Field experiments
– Controlled variables in a natural environment

• Quasi (natural*) experiments
– No control over the independent variable and Pps
cannot be randomly allocated to a condition.
– it’s ‘naturally’ occurring (eg Gender)
* Do not get this confused with a Field experiment!


5



6

Research investigating if there is a
difference between students who
are deprived of sleep and students
who have had plenty of sleep.



7

An experiment to investigate if men
are more obedient than women
when an experimenter asks them to
inflict pain onto another person.



8

A study to investigate if people on a
train travelling from Hull to York
would help someone who falls over
more if they were dressed as a
disabled person or a drunk.


9

We want to investigate if a person
will remember images or words
better having been exposed to them
for thirty seconds.



10

Will white rats be able to run a maze
quicker than grey rats?



11

Experiments
cause

effect

Independent
Variable
(IV)

Dependent
Variable
(DV)



12

Task
Based on the way the research
questions are written complete the
Independent Variable (IV) and
Dependent Variable (DV) boxes only.
You can work in pairs if you wish.

Time: 10 minutes


13

Experiments
cause

effect

Independent
Variable
(IV)

Dependent
Variable
(DV)

Confounding Variable: a variable that effects the DV
Extraneous Variable: a variable that could affect the DV but
has been controlled for so it doesn’t.



14

• independent variable: that variable that is being
manipulated; the difference between the
experimental conditions.
• dependent variable: the variable that is being
measured by the experimenter.
• extraneous variable: a variable which could affect
the dependent variable but which is controlled so
that it does not become a confounding variable.
• confounding variable: a variable which has an
unintentional effect on the dependent variable.


15

Review
Using your course reader (pg. 54-57)
make a review sheet on the types of
experiment. Ensuring you have notes
on laboratory, field and quasi
experiments.
You can choose how you want to lay it
out. Some ideas:
•Mind map
•Full notes
•Tri-page fold –type-thing


16

Design your own …
Choose 5 of the experiments from last
lesson’s handout. For each of these consider:
a)How would you design the experiment?
What would the procedure be?
b)What experiment type would you use and
why?
c)What experimental design would you use
and why?
d)What other measures would you use to
control for confounding variables?

How science works



18

Learning Objectives


• Must be able to list the ethical issues in
psychological research.
• Should be able to describe the different types of
controls in psychological research.



19

“[The studies] are often
brilliantly controlled and
scientifically
rigorous but
bear as much
resemblance to
[real life] as an Oxo
cube does to a cow.
Such studies can be
described as
impeccable trivia.”
Banyard and Grayson, 2008


20

refe
rs to
arte
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xper
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imen
an in re pa
ta l
the
rticip
terp
expe
ants
reta
and
rime
tion
unc
nt's
of
onsc
their
purp
ious
ose
beh
acco
ly ch
avio
ur
rdin
ang
gly
e

The experimenter
The experimenter
effect is a term used
effect is a term used
to describe subtle
to describe subtle
cues or signals from
cues or signals from
an experimenter
an experimenter
that affect the
that affect the
performance of
performance of
participants in
participants in
studies.
studies.
The cues may be unconscious nonverbal cues,
The cues may be unconscious nonverbal cues,
such as muscular tension or gestures. They
such as muscular tension or gestures. They
may be vocal cues, such as tone of voice.
may be vocal cues, such as tone of voice.

Ethics



31

•
•
•
•
•

Consent
Deception
Debriefing
Withdrawal
Confidentiality


•
•
•
•

Protection
Observation
Advice
Colleagues


32

Landis (1924)
Participants required to behead a live rat with a butchers knife

Johnson et al. (1939)
Children deliberately pressured psychologically to induce
stuttering resulting in lifelong emotional suffering

Sheridan & King (1939)
Participants required to administer electric shocks to
puppies to such an extent that death occurred

Willowbrook (1956)
Children fed extracts of stool from individuals infected
with hepatitis


33

The Ethics Love Affair
How to remember the ethical guidelines

A pair of consenting adults were deceiving
their partners and having a love affair even
after their colleagues had advised them not
to. They had gone to the park to ‘make love’
so they debriefed but they didn’t have any
protection so he had to withdraw. Some perv
was observing and told everyone about it and
their affair was confidential no more.


34

Task

Some experimental
Questions!
You can use your
personal notes or course
reader.
Time: 20 minutes


35

How science works



36

Learning Objectives

• Must be able to do this …
• Should be able to do that …
• And maybe, if you’re good, do this …



37

Experiments
• Independent
Measures
• Participants are only
in one condition.
Condition 1 Condition 2

Repeated Measures
• The same participants
repeat the two
conditions
Condition 1

Condition 2

Counter balancing – alter order of Pp’s


38

Experiment
independent
groups or repeated
measures?



39

Independent Groups
Remember these
Banana

Potato

Sweetcorn Pear

Tomato

Pineapple

Turnip

Apricot

Grape

Carrot

Apple

Strawberry



40

Apricot

Broccoli

Onion

Strawberry Tomato

Pineapple

Banana

Sweetcorn Orange

Carrot

Turnip

Lettuce

Apple

Lemon

Raisin

Potato

Blackberry


Pear


Grape
Cucumber

41

Repeated Measures
Remember these
Television Chair

Curtain

Video

Wall

Clock

Table

Sink

Bin

Desk

Shelf

Stool



42

Video

Alarm

Frame

Television Box

Wall

Table

Stool

Chair

Desk

Shelf

Curtain

Sofa

Heater

Picture

Clock

Carpet

Sink


Bin


Window

43

Strength

Weakness

Independent
Measures

No Order Effects
Fewer Demand
Characteristics

Individual
Differences

Repeated
Measures

No Individual
Differences

Order Effects
(counter balancing)

Evaluation of Experimental Designs



44

Experiments
Matched Pairs – make two groups of participants
as similar as possible.
Condition 1

Condition 2
Male
21
IQ = 105

Male
21
IQ = 105

Female
25
IQ = 115


Female
25
IQ = 115

45

Strength

Weakness

Independent
Measures

No Order Effects
Fewer Demand
Characteristics

Individual
Differences

Repeated
Measures

No Individual
Differences

Order Effects

Matched
Pairs

Controls for
Individual
Differences

(counter balancing)

Can be difficult
and costly.

Evaluation of Experimental Designs


46

Validity

Reliability

Check

Different
methods to
collect DV

Replicate

Improve

Improve DV
method

Improve
Controls



47



48

Sampling
Representative Sample
Generalisations

General Population

Sampling Techniques

Sample

Sampling
Opportunity Sample

Random Sample

• People who are there at
the time.

• Each person in the GP
has an equal chance of
being chosen.

• Quick / Cheap / Easy
• Not representative

• Expensive and time
consuming.
• Representative sample

Sampling
Self-Selected

Snowball Sampling

• Participants volunteer to
be in the sample following
advert etc.

• One person tells others
who tell others …

• Quick / Cheap / Easy
• Not representative
What kind of person volunteers
for a psychology experiment?

• Allows us to collect
difficult to locate people.
• Time consuming.

The population is the group of people from whom the
sample is drawn.
For example if the sample of participants is taken from
sixth form colleges in a city, the findings of the study
can only be applied to that group of people and not all
sixth form students in the UK and certainly not all
people in the world.


52

Obviously it is not (usually) possible to test everyone in the
target population so therefore psychologists use sampling
techniques to choose people who are representative (typical)
of the population as a whole.

=
If your sample is representative then you can generalise
the results of your study to the wider population.


53

Geek
!

Want to
be in my
study?

Opportunity sampling is the sampling technique most
used by psychology students. It consists of taking the
sample from people who are available at the time the study
is carried out and fit the criteria you are looking for.


54

This is a sampling technique which is defined as a sample
in which every member of the population has an equal
chance of being chosen.


55

Volunteerslove
I just needed for
Sounds
I’ve
Gotta do
psychological studyalways
to be
rubbish…hair..
wanted to be in
my
helpful….
on learning
a study….

Self selected sampling (or volunteer sampling) consists of
participants becoming part of a study because they volunteer
when asked or in response to an advert.


56

= 60% female
40% male

= 60% female
40% male

Stratified sampling involves classifying the population into
categories and then choosing a sample which consists of
participants from each category in the same proportions as
they are in the population.


57

Experiments – Hypotheses
How are we
measuring
memory?

What’s better or
worse? Higher /
Lower? More / Less?

Participants memory will be much worse
when there is a distraction in the room than
What is the
when there is no distraction.
distraction? How are
we manipulating it?

Operationalising your hypothesis
How have you manipulated your IV?
How have you measured your DV?


58

Participants memory will be much worse
when there is a distraction in the room than
when there is no distraction.
Participants will remember significantly
more words from a list of 20 presented for
60 seconds when they are in a room with
no distractions than participants who are in
a room where rock music is playing in the
background.


59

Alternate

Participants who [do something] will be
significantly [faster/better/quicker etc] at
[something] than participants who [do
something else].

Null


There will be no significant difference
between participants who [do something]
and those who [do something else]. Any
difference will be down to chance.



60

1Tailed

Participants who [do something] will be
significantly [faster/better/quicker etc] at
[something] than participants who [do
something else].

2Tailed

There will be a significant difference
between participants who [do something]
and those who [do something else].



61

Independent &
Independent &
Dependent Variables
Dependent Variables

Confounding &
Confounding &
Extraneous Variables
Extraneous Variables

Types of
Types of
Experiments
Experiments
Laboratory
Laboratory
Field
Field
Quasi (natural)
Quasi (natural)

Sampling
Sampling
Methods
Methods

Opportunity
Opportunity
Random
Random
Snowball
Snowball
Stratified
Stratified
Self-Selected
Self-Selected

Experiment
Experiment
al Methods
al Methods

Cause &
Cause &
Effect
Effect
Independent
Independent
Measures
Measures
Repeated Measures
Repeated Measures
Matched-Pairs
Matched-Pairs

Ethics
Ethics
Ecological Validity
Ecological Validity
Reliability
Reliability
Validity
Validity

±
62

Key Terms - Experiments
•
•
•
•
•
•
•
•
•
•
•

Laboratory Experiment
Field Experiment
Quasi Experiment
Independent Variable
Dependent Variable
Confounding Variable
Extraneous Variable
Replication
Cause and Effect
Ecological Validity
Alternate Hypothesis


•
•
•
•
•
•
•
•
•

Demand Characteristics
Ethics
Independent Measures
Repeated Measures
Matched-Pairs
Individual Differences
Order Effects
Counter Balancing
Operationalising
Hypothesis
• Null Hypothesis


63

Data Analysis
Nominal - measure of central tendency: mode
Data in categories (finished, fell, started)
Ordinal - measure of central tendency: median
Data which are ranked or in order (1st 2nd 3rd)
Interval - measure of central tendency: mean
Precise and measured using units of equal intervals
(1m54s, 1m59s, 2m03s)
Measure of dispersion = range (Highest – Lowest)


64

Levels of Measurement
•
•
•
•

Time
Weight
Length
Number of ‘keepieups’
• Age (years old)


• Colours
• Score on a test
• Extroversion score on
a scale of 1-10
• Money
• Age (young /
teenager / middle age
/ old)


65

Descriptive Statistics
measurement of central tendency (average)
measurement of dispersion (range or standard deviation)
graphs & visual displays

Inferential Statistics
statistical tests – making inferences from the results



66

Which Statistical Test?
NOMINAL
DATA

ORDINAL
DATA

INTERVAL
DATA

REPEATED
MEASURES

Sign test

Wilcoxon sign test

Related t
test*

MATCHED
PAIRS

Sign test

Wilcoxon sign test

Related t
test*

INDEPENDENT
MEASURES

Chi-squared

Mann-Whitney
'U'

Unrelated t
test*

CORRELATION

Chi-squared

Spearman
Rho

Pearson
moment*



67

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