The Process of Data The Process of Data AnalysisAnalysis

February 14, 2011February 14, 2011

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ObjectivesObjectivesBy the end of this meeting, participants By the end of this meeting, participants

should be able to:should be able to:

a)a) Describe the various ways in which Describe the various ways in which causality can occur and draw causal causality can occur and draw causal diagrams.diagrams.

b)b) Develop a hypothesis based on a causal Develop a hypothesis based on a causal theory and explain the necessary theory and explain the necessary considerations for testing a hypothesis.considerations for testing a hypothesis.

c)c) Distinguish variables by their level of Distinguish variables by their level of measurement.measurement.

d)d) Define Type I and Type II error and Define Type I and Type II error and explain why they should be avoided.explain why they should be avoided.

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How to Start Data AnalysisHow to Start Data Analysisa)a) Decide whether you are interested in Decide whether you are interested in

a descriptive or explanatory analysisa descriptive or explanatory analysisb)b) If you decide on the latter, state at If you decide on the latter, state at

least one hypothesis (could be least one hypothesis (could be several)several)

c)c) Carefully identify your variables or Carefully identify your variables or predictorspredictors• Independent (a cause or a predictor)Independent (a cause or a predictor)• Dependent (a result)Dependent (a result)

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Thinking about CausationThinking about Causationa)a) Causation can occur in many waysCausation can occur in many ways• DirectDirect• IndirectIndirect• MultipleMultiple• ReciprocalReciprocal

b)b) Due to the fact that the most Due to the fact that the most interesting phenomenon frequently interesting phenomenon frequently have different types of causes, have different types of causes, researchers frequently draw causal researchers frequently draw causal diagramsdiagrams

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Testing a Causal HypothesisTesting a Causal HypothesisFour tests are necessary for an Four tests are necessary for an

independent variable to cause a independent variable to cause a change in a dependent variablechange in a dependent variable

a)a) AssociationAssociationb)b) Temporal orderTemporal orderc)c) Need to consider alternative causesNeed to consider alternative causesd)d) Causal MechanismCausal Mechanism• South Korean attitudes towards South Korean attitudes towards

contraceptives and appliance ownershipcontraceptives and appliance ownership• Homicide rate and ice cream salesHomicide rate and ice cream sales

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Operationalizing ConceptsOperationalizing Conceptsa)a) Researchers must find a way to Researchers must find a way to

change concepts that they seek to change concepts that they seek to measure into tangible variablesmeasure into tangible variables

b)b) For example, if you believed that For example, if you believed that wealth impacted vote choice, how wealth impacted vote choice, how should that concept be should that concept be operationalized? operationalized?

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Levels of MeasurementLevels of Measurementa) Nominal Variables: Distinct categories

that are not related in any numerical or orderly fashion. (No order)• Ex: respondents’ religion, region of the

country, or race

b) Ordinal Variables: Ordered categories that do not have any intrinsic numerical qualities. (Ordered but uneven intervals)• Ex: SA, A, N, D, SD or 1st , 2nd , 3rd , 4th

• Party?

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Levels of MeasurementLevels of Measurementa) Interval Variables: Intrinsically

numeric but lack a meaningful zero point; distance between successive numbers are equal. (Ordered and even intervals)• Ex: Fahrenheit scale or Celsius scale

b) Ratio Variables: Intrinsically numeric with a meaningful zero point. (Ordered, even intervals, and a meaningful zero point)• Ex: Age, height, and income

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Hypothesis TestingHypothesis Testinga) Hypothesis (H): Eating ice cream builds

muscle mass.b) Fallacy of affirming the consequent: I am

stronger; it must be from eating ice cream.c) Denying the consequent: If I am not

stronger, I couldn’t have eaten any ice cream.

d) A research hypothesis cannot be proven, only disproven.

e) If I eat more ice cream and I get stronger, it does not mean that eating ice cream builds muscle mass.

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Hypothesis TestingHypothesis Testinga) Null Hypothesis (Ho): Opposite of the

research hypothesis. In this case, no relationship exists between eating ice cream and building muscle.

b) My hypothesis predicts that we will reject the null hypothesis.

c) Rejecting the null hypothesis does not prove the research hypothesis. Rather, by offering evidence that the null is not true, the researcher shows that the research hypothesis may be true.

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Types of ErrorTypes of Errora) Type 1 Error: Reject (incorrectly) a true

null hypothesis. • The null hypothesis (that no relationship exists)

is true. Our analysis, however, incorrectly leads us to conclude that a relationship exists.

b) Type 2 Error: Accept (incorrectly) a false null hypothesis.• The null hypothesis (that no relationship exists)

is false. Our analysis, however, incorrectly leads us to conclude that no relationship exists.

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Statistical InferenceStatistical Inferencea)a) Researchers need to how much Researchers need to how much

chance of being incorrect are they chance of being incorrect are they willing take. willing take.

b)b) The standard acceptable Type I Error The standard acceptable Type I Error in the social sciences is .05. in the social sciences is .05.

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For Next TimeFor Next Timea)a) Read WKB chapter 9.Read WKB chapter 9.b)b) Open the class poll from j.mp/pubOpinOpen the class poll from j.mp/pubOpinc)c) Using the variables from the poll, derive three Using the variables from the poll, derive three

distinct hypotheses and identify what level of distinct hypotheses and identify what level of measurement the variables are (nominal, measurement the variables are (nominal, ordinal, interval, ratio) ordinal, interval, ratio) • Hypotheses need to clearly state a possible Hypotheses need to clearly state a possible

relationship between variables in the class surveyrelationship between variables in the class survey• Levels of measurement need to reflect the Levels of measurement need to reflect the

questions as asked on the survey (not how they questions as asked on the survey (not how they could have been asked).could have been asked).

• Think about a causal mechanism. (DonThink about a causal mechanism. (Don ’’t have to t have to write that out right now.)write that out right now.)