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Outline and readings for Lecture 3
Key topics addressed
*Anecdotal evidence and its problems
*Correlation*Independent and Dependent Variables
*Types of research design: Correlational, Quasi-Experiment, True Experiment
*External Validity
*Internal Validity
*The need for a control condition
*Blinding
Recommended reading:* Taylor, James. Efficacy and safety of Echinacea in treating upper respiratory tract infections in children: A
randomized controlled trial.
PDF is on library website, direct link is:http://opac.library.usyd.edu.au/search~S4?/rpsyc1001/rpsyc1001/1,1,1,B/frameset~3140013&FF=rpsyc1001&1,1,
NB: If this link or any other library article link does not work, go to the library website: http://www.library.usyd.edu.au/
Then CATALOGUE, select Unit of Study, and type in PSYC1001. You will find a page of articles and this one will be one of them.
Recommended media:
Enemies of Reason BBC 2008 download from Blackboard (from the front page Videos related to
Psychology lectures and tutorials). It is 44minutes for this lecture it is the section on Dowsing which will
be specifically referred to 24:40 29:40.
http://opac.library.usyd.edu.au/search~S4?/rpsyc1001/rpsyc1001/1,1,1,B/frameset~3140013&FF=rpsyc1001&1,1http://www.library.usyd.edu.au/http://www.library.usyd.edu.au/http://opac.library.usyd.edu.au/search~S4?/rpsyc1001/rpsyc1001/1,1,1,B/frameset~3140013&FF=rpsyc1001&1,17/30/2019 Calebs 2013 Stats Lecture 3
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Science & Statistics in Psychology
Lecture 3
A thousand zeros is still nothing
Dr Caleb Owens
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Lecture Outline
Research designsAnecdotes and case studies Correlational studies
Quasi-experiments
True experiments
External validity
Random sampling
Internal validity Random allocation
Blinding
Even more terminology Independent
variable
Dependent variable Control condition
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Baby got sick anecdote
Hypotheses:Change in formula
Virus
Change in weather
Local water supply
Teething
Requires solids
Important points:Anecdote may only contain
one possible cause
What advice would I give to
other parents and how would I
qualify that advice?
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Condition ParticipantParticipant Participant Participant Participant Participant Participant Participant
No change
in formula
1 2 3 4 5 6 7 8
Aust
Formula ->Japan
Formula
9 10 11 12 13 14 15 16
Japan
Formula ->
Aust
Formula
17 18 19 20 21 22 23 24
24 babies (8 per condition) needed for a controlled test of just ONE
hypothesis
Why would we think that our observations of ONE baby would be
enough to distinguish between SIX plausible hypotheses?
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Anecdotal evidence
The plural of anecdote is not evidence
Anecdotes are usually worse than useless
Because they generally support what we believe
The anecdote contains the (proposed) explanationwhich cannot be untangled once it is passed on
It cannot be replicated or documented by non-
prejudiced observers
It changes with every retelling and depends on falliblememory
At most anecdotes provide clues and leads
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I got better anecdote
I am living proof that X works
I had illness Y, and was treated with X, and then
I got better!
So it must have been X !!!
What is wrong with this conclusion?
What else could have happened?
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Case studies
Significantly more systematic than anecdotes All details taken and recorded in a scientific manner
May simply consist of the combination of previouslycollected information
Can consist of the systematic collection of longitudinaldata E.g. The famous television series: 7-up, 49-up
Provide important details which can lead to latersystematic research and breakthroughs
Should not be over-interpreted since the sample size isoften small and rarely randomly selected Ideal for investigating rare or highly specific topics
E.g. prosopagnosia
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Anecdote
My Aunty Liz got Cholera fromthe terrible smells and gases
coming from the river near herhouse. She moved house.Whenever she smellssomething bad from now onshe stays away and hasnt gotCholera since!
Case Study
Elizabeth Cromwell contractedCholera on 12th July 1723
during a particularly hotsummer.
When winds were blowingfrom the East, her housebecame filled with noxiousgases causing a terrible smell.
She was an otherwise healthywomen whose only otheraffliction was mild Dysenterysome years earlier.
Her house was located next tothe river Thames which at thetime contained a large amountof raw sewage.
She drew her drinking waterfrom a well which was exposedto the river.
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Correlational studies
Measure two naturally occurring variables Find a relationship between them
Only a very weak causal inference could
be drawn (a suggestion, a lead for moreresearch)
No independent variables are controlled
e.g. Simply look through lots of data and find
relationships
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Correlation Coefficients
XY = 0.7
The sign (+ or ) indicates
the direction of the
relationship(+ : as values on one variable get bigger,values on the other get bigger; - : as values
on one variable get bigger, values on the
other get smaller)
The number indicates
the strength of the
relationship(0.1, 0.2, 0.3 = weak ;
0.7, 0.8, 0.9 = strong)
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Scatterplots
X
100806040200
Y
600
400
200
0
-200
-400
-600
X
100806040200
Y
120
100
80
60
40
20
0
-20
XY = 0.25
XY = 0.88Positive Correlations
The score on two
IQ tests taken on
the same day
The relationshipbetween High
School grades
and University
grades
Each person has two scores and these
are plotted on separate axes
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Scatterplots
X
100806040200
Y
20
0
-20
-40
-60
-80
-100
XY = -0.93
X
100806040200
Y
400
300
200
100
0
-100
-200
-300
-400
XY = -0.16
Negative Correlations
The number of
hours of exercise
people do and their
excess fat in a
pinch test
The amount of
time people
spend on the
internet and their
university grades
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Correlation and Causation
Just because two variables are correlated
with each other does not mean that one
causes the other.
Example: The number of ice-creams
consumed on a certain day correlates
positively with deaths by drowning (0.8)
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Correlation and Causation
It could be that:
Eating ice-cream causes drowning
Drowning causes ice-cream to be eaten
Amount of ice-cream eaten and number ofdrownings are both caused by the
temperature on a particular day
Does the cold of winter cause colds andflu ?
http://www.straightdope.com/columns/read/997/why-is-winter-the-season-for-colds-flu-etc
http://www.straightdope.com/columns/read/997/why-is-winter-the-season-for-colds-flu-etchttp://www.straightdope.com/columns/read/997/why-is-winter-the-season-for-colds-flu-etchttp://www.straightdope.com/columns/read/997/why-is-winter-the-season-for-colds-flu-etchttp://www.straightdope.com/columns/read/997/why-is-winter-the-season-for-colds-flu-etchttp://www.straightdope.com/columns/read/997/why-is-winter-the-season-for-colds-flu-etchttp://www.straightdope.com/columns/read/997/why-is-winter-the-season-for-colds-flu-etchttp://www.straightdope.com/columns/read/997/why-is-winter-the-season-for-colds-flu-etchttp://www.straightdope.com/columns/read/997/why-is-winter-the-season-for-colds-flu-etchttp://www.straightdope.com/columns/read/997/why-is-winter-the-season-for-colds-flu-etchttp://www.straightdope.com/columns/read/997/why-is-winter-the-season-for-colds-flu-etchttp://www.straightdope.com/columns/read/997/why-is-winter-the-season-for-colds-flu-etchttp://www.straightdope.com/columns/read/997/why-is-winter-the-season-for-colds-flu-etchttp://www.straightdope.com/columns/read/997/why-is-winter-the-season-for-colds-flu-etchttp://www.straightdope.com/columns/read/997/why-is-winter-the-season-for-colds-flu-etchttp://www.straightdope.com/columns/read/997/why-is-winter-the-season-for-colds-flu-etchttp://www.straightdope.com/columns/read/997/why-is-winter-the-season-for-colds-flu-etchttp://www.straightdope.com/columns/read/997/why-is-winter-the-season-for-colds-flu-etchttp://www.straightdope.com/columns/read/997/why-is-winter-the-season-for-colds-flu-etc7/30/2019 Calebs 2013 Stats Lecture 3
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Some plausible correlational findings
Living close to the beach is correlated with being rich Causation in the other direction ?
Religiousness is correlated with being on death row Causation in the other direction ? Third variable ?
Arriving illegally by boat is correlated with being violent Third variable ?
Being at University is correlated with being homosexual Measurement bias ?
Height is correlated with IQ Third variable ?
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Correlation and Causation
In general, if A & B are correlated it ispossible that:
A causes B
B causes A
Some other variable C causes both A & B
Correlation Causation!
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http://news.yahoo.com/s/yblog_upshot/20101012/bs_yblog_u
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ts-decomposition-for-six-months
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/news.yahoo.com/s/yblog_upshot/20101012/bs_yblog_upshot/mcdonalds-happy-meal-resists-decomposition-for-six-monthshttp://news.yahoo.com/s/yblog_upshot/20101012/bs_yblog_upshot/mcdonalds-happy-meal-resists-decomposition-for-six-monthshttp://news.yahoo.com/s/yblog_upshot/20101012/bs_yblog_upshot/mcdonalds-happy-meal-resists-decomposition-for-six-monthshttp://news.yahoo.com/s/yblog_upshot/20101012/bs_yblog_upshot/mcdonalds-happy-meal-resists-decomposition-for-six-monthshttp://news.yahoo.com/s/yblog_upshot/20101012/bs_yblog_upshot/mcdonalds-happy-meal-resists-decomposition-for-six-monthshttp://news.yahoo.com/s/yblog_upshot/20101012/bs_yblog_upshot/mcdonalds-happy-meal-resists-decomposition-for-six-monthshttp://news.yahoo.com/s/yblog_upshot/20101012/bs_yblog_upshot/mcdonalds-happy-meal-resists-decomposition-for-six-monthshttp://news.yahoo.com/s/yblog_upshot/20101012/bs_yblog_upshot/mcdonalds-happy-meal-resists-decomposition-for-six-months7/30/2019 Calebs 2013 Stats Lecture 3
19/39
http://www.n
aturalnews.com/030074_H
appy_Meal_decompose.html
http://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.htmlhttp://www.naturalnews.com/030074_Happy_Meal_decompose.html7/30/2019 Calebs 2013 Stats Lecture 3
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Source:http://aht.seriouseats.com/archives/2010/11/the-burger-lab-revisiting-the-myth-of-the-12-year-old-burger-testing-results.html
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The control condition
Since variables change (or do not change)all by themselves, or by the action of
unforeseen agents, a no-manipulation, no-
drug, unaffected, control condition isneeded
This is usually one level of a manipulated
independent variable Condition 1: Drug High Strength
Condition 2: Drug Low Strength
Control Condition 3: No drug
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Independent & Dependent
Variables
Presumed Cause
Antecedent Cause
Stimulus Variable
Behaviour of Interest
Response Variable
Independent
Variable
Dependent
Variable
Manipulated by
experimenterMeasured by
experimenter
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Correlational studies
Measure two naturally occurring variables Find a relationship between them
Only a very weak causal inference could
be drawn (a suggestion, a lead for moreresearch)
No independent variables are controlled
e.g. Simply look through lots of data and find
relationships
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True Experiments Randomly allocate subjects to different levels of the
independent variable
So all independent variables of interest are controlled
By not letting subjects choose, most confounds
cancel each other out because you have a randomamount of each in each group
E.g. When subjects turn up you toss a coin to see which
condition they go into. If the experiment is based on speed,then with enough subjects, naturally fast and slow people
in each condition will cancel each other out
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Quasi-experiments Some attempt at controlling variables
Matching Manipulating some IVs but not others
Always a study of pre-existing groups in some sense
Whenever you have pre-existing groups you have
obvious confounds
Causal inference is weak
Example
When studying the psychological impact of domesticviolence, you find a control group which has not
experienced violence (and you want to ensure the groups
are as similar as possible), and you may give both groups
different kinds of therapy
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Random allocation of independent
variables
Correlational study : NONE
Quasi experiment : At least one (but not
others); or none, but some attempt to
control one (e.g. matching)
True Experiment : ALL
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Research Designs: Drug use example
Correlational: simply record the amount of alcoholconsumed and University Grades Weak causal inference
Numerous alternative explanations
Quasi-experimental: Select a group of people whodrink regularly and a group who do not, match themon diet, exercise, age and lifestyle and compare theirgrades Eliminates some confounds
Does not control for all variables (e.g. attitude, personality) True experiment: Randomly allocate 250 people to
drink heavily and 250 to drink a placebo control Controls for most extraneous variables
Puts 50% at risk !
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Research Designs: Self-Esteem Example
Correlational: Record self-esteem and University
Grades and look for a relationship Weak causal inference
Numerous alternative explanations
Quasi-experiment: take people who have high self-
esteem and low self-esteem; compare their gradesand try to improve these with extra classes or peersupport Eliminates some alternative explanations
Self-esteem is still pre-existing and may have been caused
by a third variable True experiment: Randomly allocate 250 people to
high self-esteem and 250 people to low self-esteemand measure the impact on Uni grades Controls for most extraneous variables
Impractical, unethical
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Control means:
Being able to determine what level of the
independent variable(s) any participant willreceive
There is no control when: Participants self-select which group they are
in (e.g. Choosing a particular treatment)
Participants already belong to a level of theindependent variable because of a pre-
existing condition
The independent variable cannot be easily or
ethically changed
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Controlling variables
Hard to randomly
allocate:
Treatments
Lifestyles
Education
Experience
Diet
Impossible to randomlyallocate Sex
Brain damage (in humans)*
Psychological disorders Extreme stress / trauma
/anxiety
Sexuality
Family
Location Religion
Race
Income
*TMS, transcranial magnetic stimulation, now makes this possible
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Sex differences
Males are better than females at spatial tasks(e.g. mental rotation)
Hypothesize: Maybe this is caused by males
having more experience with spatial toys
Match males & females on Lego experience
This is called holding the variable constant: its not the
same as the control you have in a true experiment
Males are better than females at spatial tasks but
when we controlled for spatial task experience the
difference disappeared
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External validity
Based on sample size, and the representativeness ofthe sample and where and how the experiment isconducted
Depends on random selection of subjects and howclosely the setting matches the real world
How applicable is the data to the real world? How applicable to the real world are laboratory based
findings?
How well can you generalize from your results tothe real world? NB: This depends heavily on the topic
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Internal validity
The ability to draw a causal inference
The extent to which changes in the DV are
likely to be due to changes in the IV
Depends on random allocation of subjects to
different levels of the IV and the elimination of
alternative explanations and confounding
variables Type of Research Design Internal ValidityCase Study / Anecdote Zero
Correlational Study Very low or zero
Quasi-Experiment Low to moderate
True Experiment High
Bli d
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Blindness Being blind means you do not know what
treatment/condition is being administered
If the researcher is not blind May not randomly allocate correctly
May unconsciously change data
May unconsciously record data and affect outcome
If the subject is not blind The effect arises because they expect it to (placebo effect)
If both subject and experimenter dont know whatcondition is being administered it is called double-blind
Could anecdotal evidence ever be of a randomized
double blind nature?
Unblinded
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Unblinded
Participant takes a pill knowing that it is intended to
relieve pain
Single-blind Participant is given a pill by a researcher (who knows
what it does) but is not told whether or not it will
relieve pain
Double-blind Researcher 1 makes the pills Yellow and Blue. She
gives them to Researcher 2 who does not know which
one has an active ingredient. Researcher 2 gives the
participant one of the pills and records how effective itis. Researcher 1 takes the data which records how
effective the Yellow and Blue pills were and makes a
conclusion (only they knew that the Blue pill
contained an active ingredient)
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Clever Hans
-see http://en.wikipedia.org/wiki/Clever_hans
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Dowsing: the ideomotoreffectSee video: Enemies of Reason Episode 1, 24:40-29:40
Download from Blackboard
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Replication
Beyond the design, replication is everything inscience
Replication means the same findings can be foundagain by repeating the study
This is why in an APA formatted research article the Methodsection goes into enough detail to repeat the study
Beware of people and websites who pick out just ahandful of (often older) articles to support their view,
and ignore the fact such results were never foundagain, or are found very rarely (indicating a result dueto chance or bias)
Beware of groups who insist their results can only bereplicated by people who are trained in doing what
they do
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Summary
Be able to distinguish between and define theseresearch designs: Case-study
Correlational study
Quasi Experiment True Experiment
Understand this important terminology External Validity
Random Selection Internal Validity
Random Allocation
Replication
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