THE SCIENTIFIC METHODWhy psychology is a science

How do we know things

Think of something about the world that you just know is correct

Cooking at home is cheaper than eating out in a restaurant

It’s better to punt on 4th down and long than try to get the 1st down

Tornados never happen during the winter

How we know things• Sources of declarative knowledge• Authority

9/10 dentists say flossing daily prevents cavity formation

Your mom tells you that you need good grades to get into college…

How we know things• Sources of declarative knowledge• Authority• Common sense/common knowledge

Swimming immediately after eating causes cramps

Playing violent video games causes violent behavior

How we know things• Sources of declarative knowledge• Authority• Common sense/common knowledge• Intuition

Food poisoning attributed to new/novel foods

Your cat ruins your stuff because he is mad at you

How we know things• Sources of declarative knowledge• Authority• Common sense/common knowledge• Intuition• Empiricism

How we know things• Sources of declarative knowledge• Authority• Common sense/common knowledge• Intuition• Empiricism

Not mutually exclusive

What is empiricism?• Knowledge must be grounded in observations• These observations are gathered through the use of the scientific method

Set of techniques that allow for the evaluation of ideas based on evidence

What is empiricism?• Knowledge must be grounded in observations• These observations are gathered through the use of the scientific method

Application of the scientific method

Generate theory

Articulate

hypothesis

Make predictio

nDesign study

Interpret results

Gather data

Share findings

theoretical

experimental

analytical

The scientific method

Generate theory

Articulate

hypothesis

Make predictio

nDesign study

Interpret results

Gather data

Share findings

theoretical

Theories, hypotheses, and predictions• Main components of the scientific method• Theory: a model that potentially explains a set of

observations/phenomena• Does NOT mean that the explanation is lacking evidence• Has different meanings in science compared to everyday language

The ‘theory’ of evolution

The ‘theory’ of gravity

Theories, hypotheses, and predictions• Main components of the scientific method• Theory: a model that potentially explains a set of

observations/phenomena• Does NOT mean that the explanation is lacking evidence• Has different meanings in science compared to everyday language

The ‘theory’ of gravity

Theories, hypotheses, and predictions• Main components of the scientific method• Theory: a model that potentially explains a set of

observations/phenomena

The burning sensation on your tongue after eating spicy foods is caused by chemicals in the peppers that bind to your taste buds

Theories, hypotheses, and predictions• Main components of the scientific method• Theory: a model that potentially explains a set of

observations/phenomena

• Hypothesis: idea about how the world operates that follows directly from a theory• Suggests some systematic, predictable pattern between phenomena

Ingesting foods that cause these chemicals to ‘let go’ of your taste buds will soothe the burning feeling on your

tongue

Theories, hypotheses, and predictions• Main components of the scientific method• Theory: a model that potentially explains a set of

observations/phenomena

• Hypothesis: idea about how the world operates that follows directly from a theory

• Prediction: forecast of how data will come out in a particular study• Specific only to the study in question, not generalized to other

situations

Theories, hypotheses, and predictions• Main components of the scientific method• Theory: a model that potentially explains a set of

observations/phenomena• Does NOT mean that the explanation is lacking evidence• Has different meanings in science compared to everyday language

• Hypothesis: idea about how the world operates that follows directly from a theory• Suggests some systematic, predictable pattern between phenomena

• Prediction: forecast of how data will come out in a particular study• Specific only to the study in question, not generalized to other

situations

general

specific

Theories, hypotheses, and predictions• Parental Investment Theory• Theory: The sex with smaller obligate parental investment will compete

for access to the sex with larger obligate investment

Trivers, 1972

Theories, hypotheses, and predictions• Parental Investment Theory• Theory: The sex with smaller obligate parental investment will compete

for access to the sex with larger obligate investment

Trivers, 1972

Theories, hypotheses, and predictions• Parental Investment Theory• Theory: The sex with smaller obligate parental investment will compete

for access to the sex with larger obligate investment

• Hypothesis: The higher investing sex will be more selective in choosing mating partners than the lower investing sex

• Prediction: men will be more likely to agree to sleep with a stranger than will women

Trivers, 1972 Clark & Hatfield, 1986

“Will you go to bed with me tonight?”

“Will you go out on a date with me tonight?”

Theories, hypotheses, and predictions

Women

Men

Go on a date tonight Go to bed with me tonight

~50% 0

~50% 75%

Theories, hypotheses, and predictions• The most important property of theories, hypotheses, and

predictions is that they are falsifiable• Must be some data that can disconfirm prediction

✔ ✖Get better

Too far gone for treatmentDieDie

Theories, hypotheses, and predictions• The most important property of theories, hypotheses, and

predictions is that they are falsifiable• Must be some data that can disconfirm prediction

Get what you imagine Don’t get what you imagine

✔ ✖Don’t get what you imagine

Didn’t believe hard enough

The scientific method

Generate theory

Articulate

hypothesis

Make predictio

nDesign study

Interpret results

Gather data

Share findings

experimental

Testing predictions• Need tools to measure the dimensions that are of interest

Imagine you are testing the hypothesis that stronger people are quicker to anger than weaker people

How would you measure strength? How would you measure anger?

Testing predictions• Need tools to measure the dimensions that are of interest• Require operational definitions – concrete, measureable descriptions of

the dimensions of interest in a study

• Good operational definitions:• do not rely on subjective judgments• make it easy for others to exactly replicate• have high reliability• have high construct validity

ReliabilityDoes a measure produce the same results when repeated under the same conditions?

“consistency”

Construct validityDoes a measure actually measure the dimension you want it to?

“accuracy”

• Reliability vs. validity

Operational definitionsCould be survey, physiological measurement, reaction time

task, etc

• Reliability vs. validity

240 lbs.(actual weight) average = 220.6

Mon Tues Weds Thurs Fri

221 219 220 221 222

Operational definitions

☐ validity

☐ reliability✗✓

• Reliability vs. validity

240 lbs.(actual weight) average = 240.8

Mon Tues Weds Thurs Fri

230 241 231 248 254

Operational definitions

☐ validity

☐ reliability✗✓

• Reliability vs. validity

240 lbs.(actual weight) average = 240.2

Mon Tues Weds Thurs Fri

240 241 241 240 239

Operational definitions

☐ validity

☐ reliability✓✓

Next time…• Research designs