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Lecture 2

PSYCH 9A Lecture Notes - Lecture 2: Effect Size, Internal Validity, Statistical Significance

Cognitive Sciences
Course Code
Thomas Michael D' Zmura

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Making Observations
Look for patterns within our observations  variables- any characteristic whose values
can change
Defining the Question
Guided by questions we hope to address through our observations
Formulate the question in a way that leaves no doubt about how we’re going to link the
question to the evidence we collect
Testable hypothesis- a prediction that has been formulated specifically enough so that it
is clear what observations would confirm the prediction and what observations would
challenge it
oTestability guaranteed by ensuring the hypothesis is falsifiable
To address a question, we need to develop an operational definition- a definition that
translates the variable we want to assess into a specific procedure or measurement
Dependent variable- variable that is measured or recorded in an experiment;
independent variable- variable that the experimenter manipulates as a basis for making
predictions about the dependent variable
Systematically Collecting Data
Memories are often selective; confirmation bias
Anecdotal evidence (evidence that involved 1-2 cases) not used to draw conclusions
Defining the Sample
Psychologists often want their conclusions to apply to a particular population- the entire
group about which the investigator wants to draw conclusions
oInvestigators study only a sample- the subset of a population that the investigator
studies in order to learn about the population at large
Because each person is different from one another  random sampling- a procedure in
which every member of the population has an equal chance of being picked to
participate in a study
oOther approaches:
If want to examine how diverse population is  maximum variation
sampling (deliberately seek out unusual cases)
Case study- an intensive study of one person
H.M. – most studied man in history, suffered memory deficits
Phineas Gage – frontal lobe damage
Assessing External Validity
If we want our study to reflect the broader world, we need to ensure its external validity-
the degree to which a study’s participants, stimuli, and procedures adequately reflect the
world as it actually is
oSample of people in study must be representative of the broader population
Monitoring Demand Characteristics
Demand characteristics- the cues in a study that might tell a research participant what
behaviors are expected or desirable in that setting
To minimize a study’s demand characteristics:
o1. Try to phrase questions as neutrally as possible
o2. Treat all study participants alike
Double-blind design- the technique of assigning participants to
experimental conditions while keeping both the participants and the
researchers unaware of who is assigned to which group
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