Thinking Critically Thinking Critically with Psychological with Psychological

ScienceScience

Chapter 1Chapter 1

1

Thinking Critically …Thinking Critically …

ExperimentationExploring Cause and Effect

Evaluating TherapiesIndependent and Dependent Variables

2

ExperimentationExperimentation

Like other sciences, experimentation is

the backbone of psychology research. Experiments isolate

causes and their effects.

3

Exploring Cause and Effect

http://4.bp.blogspot.com/_qUFDMUpk9jE/SamaufWnPRI/AAAAAAAAP1c/AzyqEfgYdPA/s400/bizarro-animal-experimentation.jpg

Exploring Cause & EffectExploring Cause & EffectMany 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.

4Cause and effect relationship???http://www.702communications.com/~ahill/Cause%20and%20effect%20perhaps.jpg

Independent Variable v Dependent Independent Variable v Dependent VariableVariable

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 VariablesDependent 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 Independent Variable v Dependent VariableVariable

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 at-

risk 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.

7http://www.uncp.edu/home/collierw/ivdv.htm

Dependent v Independent VariablesDependent v Independent VariablesOf 100 individuals with obsessive-

compulsive 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 VariableDependent Variable?

Experimental Condition?Control Condition?

What are two operational definitions? 8

http://answers.yahoo.com/question/index?qid=20080127143317AAIw38P

Evaluating TherapiesEvaluating Therapies

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

Double-blind Procedure

Blind Procedure

The participants are uninformed about what treatment, if any, they

are receiving. (Experimental Group - treatment v Control Group -

placebo)

Charlatans – The Power of SuggestionCharlatans – The Power of Suggestion

10

Evaluating TherapiesEvaluating Therapies

Assigning participants to experimental (Breast-fed) and control (formula-fed)

conditions by random assignment minimizes pre-existing differences

between the two groups.

11

Random Assignment

ExperimentationExperimentation12

A summary of steps during experimentation.

ComparisonComparison

13

Below is a comparison of different research methods.

IMPORTANT!!!!!!!

Statistical ReasoningStatistical Reasoning

14

Statistical procedures analyze and interpret data allowing us to see what

the unaided eye misses.

Composition of ethnicity in urban locales

Describing DataDescribing Data

15

A meaningful description of data is important in research.

Misrepresentation may lead to incorrect conclusions.

Measures of Central Measures of Central TendencyTendency

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 rank-ordered distribution.

16

Measures of Central Measures of Central TendencyTendency

A Skewed Distribution

17

Salaried SalespeopleSalaried 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 VariationMeasures of VariationRange: 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

VariabilityVariabilityVariability 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 DeviationStandard Deviation

21

Thinking Critically …Thinking Critically …

Statistical ReasoningDescribing DataMaking Inferences

22

Making InferencesMaking InferencesA statistical statement of how frequently

an obtained result occurred by experimental manipulation or by chance.

23

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.

Making InferencesMaking Inferences

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

When is a Difference Significant?