Transcript Tim`s Ch 01B - matheusappsychology

Thinking Critically with
Psychological Science
Chapter 1
1
Thinking Critically …
Experimentation
Exploring Cause and
Effect
Evaluating Therapies
Independent and
Dependent Variables
2
Experimentation
Exploring Cause and Effect
Like other sciences,
experimentation is the
backbone of psychology
research.
Experiments isolate causes
and their effects.
http://4.bp.blogspot.com/_qUFDMUpk9jE/SamaufWnPRI/AAAA
AAAAP1c/AzyqEfgYdPA/s400/bizarro-animalexperimentation.jpg
3
Exploring Cause & Effect
Many factors influence our
behavior. Experiments (1)
manipulate factors that
interest us, while other
factors are kept under (2)
control.
Effects generated by
manipulated factors isolate
cause and effect
relationships.
Cause and effect relationship???
http://www.702communications.com/~ahill/Cause%20and%20effect%20perhaps.jpg
4
Independent Variable v Dependent Variable
An Independent Variable is a factor manipulated
by the experimenter. The effect of the
independent variable is the focus of the study.
(An independent variable is the presumed
cause; …..) or (What I change; …) They need
to be MEASURABLE.
A Dependent Variable is a factor that may change
in response to an independent variable. In
psychology, it is usually a behavior or a mental
process. (… the dependent variable is the
presumed effect.) (…what I observe.)
They need to be MEASURABLE.
5
Dependent v Independent Variables
 Memory
rule:
 The dependent variable
depends on the independent.
 You always hope to change
the dependent by altering the
independent.
6
Independent Variable v Dependent
Variable
The following is a hypothesis for a study.
“There will be a statistically significant
difference in graduation rates of at-risk
high-school seniors who participate in an
intensive study program as opposed to atrisk high-school seniors who do not
participate in the intensive study program.”
(LaFountain & Bartos, 2002, p. 57)
IV: Amount of time spent in
participating in intensive study
program. DV: Graduation rates.
7
http://www.uncp.edu/home/collierw/ivdv.htm
Dependent v Independent Variables
 Of 100 individuals with obsessivecompulsive disorder (OCD), 50 receive 8
weeks of an experimental drug for OCD,
while 50 are placed on a waiting list for 8
weeks. At the end of the 8 weeks, all 100
individuals are given psychological tests to
assess their level of OCD.
 What is the :
 Independent Variable
 Dependent Variable?
 Experimental Condition?
 Control Condition?
 What are two operational definitions?
http://answers.yahoo.
com/question/index?q
id=20080127143317
AAIw38P
8
Evaluating Therapies
Blind Procedure
The participants are uninformed about
what treatment, if any, they are receiving.
(Experimental Group - treatment v Control
Group - placebo)
Double-blind Procedure
In evaluating drug therapies, patients and
experimenter’s assistants should remain
unaware of which patients had the real
treatment and which patients had the placebo
treatment.
9
Charlatans – The Power of Suggestion
10
Evaluating Therapies
Random Assignment
Assigning participants to experimental
(Breast-fed) and control (formula-fed)
conditions by random assignment minimizes
pre-existing differences between the two
groups.
11
A summary of steps during experimentation.
Experimentation
12
Comparison
IMPORTANT!!!!!!!
Below is a comparison of different research
methods.
13
Statistical Reasoning
Statistical procedures analyze and interpret
data allowing us to see what the unaided eye
misses.
Composition of ethnicity in urban locales
14
Describing Data
A meaningful description of data is important
in research. Misrepresentation may lead to
incorrect conclusions.
15
Measures of Central Tendency
Mode: The most frequently occurring
score in a distribution.
Mean: The arithmetic average of scores in
a distribution obtained by adding the
scores and then dividing by the
number of scores that were added
together.
Median: The middle score in a rankordered distribution.
16
Measures of Central Tendency
A Skewed Distribution
17
Salaried Salespeople
 $20,000
 $20,000
 $25,000
 $35,000
 $200,000
What is the mode?
 What is the median?
 What is the mean?


In this instance, why
is the mean not the
best estimate of
what a salesperson
would earn?
18
Measures of Variation
Range: The difference between the highest and
lowest scores in a distribution.
Standard Deviation: A computed measure of how
much scores vary around the mean.
19
Variability

Variability refers to how much the scores
in a data set vary from each other and the
mean. The standard deviation is an index
of the amount of variability in a data set.
When variability is great, the standard of
deviation will be relatively low. When
variability is low the standard of deviation
will be smaller. Estimates of variability
play a crucial role in deciding whether the
results of a study support a researchers
hypotheses.
20
Standard Deviation
21
Thinking Critically …
Statistical Reasoning
 Describing Data
 Making Inferences
22
Making Inferences
A statistical statement of how frequently an
obtained result occurred by experimental
manipulation or by chance.
When is an Observed Difference Reliable?
1. Representative samples are better
than biased samples.
2. Less variable observations are more
reliable than more variable ones.
3. More cases are better than fewer
cases.
23
Making Inferences
When is a Difference Significant?
When sample averages are reliable and the
difference between them is relatively
large, we say the difference has statistical
significance.
For psychologists this difference is
measured through alpha level set at 5
percent.
24