# MAX 201 Quantitative Methods for the Social Sciences Controlling for a Third Variable; Developing a Research Topic.

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MAX 201 Quantitative Methods for the Social Sciences Controlling for a Third Variable; Developing a Research Topic

Univariate, bivariate, and multivariate analysis Most basic data description: statistics applied to one variable: mean, median, percentages. Most basic data description: statistics applied to one variable: mean, median, percentages. Bivariate analysis uses contingency tables to look at two variables at a time. Bivariate analysis uses contingency tables to look at two variables at a time. Introducing a third variable is called controlling or specifying the original relationship. Introducing a third variable is called controlling or specifying the original relationship.

Controlling for a third variable: sex and auto accidents Men have more accidents than women (gender is related to accident involvement) Men have more accidents than women (gender is related to accident involvement) Introduce a third variable: miles driven per year Introduce a third variable: miles driven per year Gender is related to miles driven (men drive more) Gender is related to miles driven (men drive more) Miles driven is related to accidents (the more you drive, the more likely you are to have an accident). Miles driven is related to accidents (the more you drive, the more likely you are to have an accident).

Sex & accidents: spurious relationship SEX SEX ACCIDENT Frequency ACCIDENT Frequency MILES driven MILES driven SEX SEX ACCIDENT Frequency ACCIDENT Frequency

Control Variable as an Intervening Variable Ind. Var. Control Variable Dep. Var.

Caffeine and Heart Attacks One study linked caffeine consumption with an increased of heart disease. One study linked caffeine consumption with an increased of heart disease. Study did not control for a third variable: whether patients in the smoked. Study did not control for a third variable: whether patients in the smoked. Heavy caffeine consumers also smoke. Heavy caffeine consumers also smoke. Further study revealed that smoking not caffeine was the cause of the heart disease. Further study revealed that smoking not caffeine was the cause of the heart disease. Source: Ian Ayres, Super Crunchers. NY: Bantam: 2007: pp 90-91. Source: Ian Ayres, Super Crunchers. NY: Bantam: 2007: pp 90-91.

Wealthier is Healthier For countries, a graph of mortality against income reveals that populations of richer countries live longer. For countries, a graph of mortality against income reveals that populations of richer countries live longer. For individuals within a country, higher- income individuals live longer than lower- income individuals. For individuals within a country, higher- income individuals live longer than lower- income individuals. The relationships are much more complex, however. The relationships are much more complex, however.

Wealthier is Healthier For countries, public health –sanitation and removal of waste – plays an important role. Big Medicine – vaccination and antibiotics – play a role. Individual care plays a larger role as income grows. For countries, public health –sanitation and removal of waste – plays an important role. Big Medicine – vaccination and antibiotics – play a role. Individual care plays a larger role as income grows. In poor countries, mosquitoes, AIDS, unsafe drinking water and other public health issues play a large role in mortality. In poor countries, mosquitoes, AIDS, unsafe drinking water and other public health issues play a large role in mortality. Insecticide will work to some degree on mosquitoes, but eventually mosquitoes develop a resistance. Need to remove open, stagnant pools where mosquitoes breed. Insecticide will work to some degree on mosquitoes, but eventually mosquitoes develop a resistance. Need to remove open, stagnant pools where mosquitoes breed.

Wealthier is Healthier For individuals, the relationship between health and income is more complex. For individuals, the relationship between health and income is more complex. Better utilization of knowledge about health (smoking) and more education may cause health, rather than income directly causing health. Better utilization of knowledge about health (smoking) and more education may cause health, rather than income directly causing health. Certain groups experience more stress from discrimination, low-income and that harms health. Certain groups experience more stress from discrimination, low-income and that harms health. Source: David Cutler, Angus Deaton, Adriana Lleras-Muney. “”The Determinants of Mortality.” Journal of Economic Perspectives. 20 (3) 2006: 97-120. Source: David Cutler, Angus Deaton, Adriana Lleras-Muney. “”The Determinants of Mortality.” Journal of Economic Perspectives. 20 (3) 2006: 97-120.

Controlling for a third variable: health care and party id Controlling for a third variable discussed in the chapter from the Cole book, “Sorting Out Relationships” Controlling for a third variable discussed in the chapter from the Cole book, “Sorting Out Relationships” Work through that example: Work through that example: original relationship is support of health care and party identification (10.1) original relationship is support of health care and party identification (10.1) control variable is income control variable is income different possibilities are considered different possibilities are considered

Party ID and Health Care Reform Support Health Care Reform RepublicanDemocratTotals No7337110 Yes67123190 Totals140167300 Gamma = 0.57 Democrats in general support health care reform; republicans show no discernable (statistical) pattern of support or opposition.

Party ID and Health Care Reform Income: LowIncome: High Support Health Care RDTotalsRD No332760401050 Yes27113140401050 Totals601402008020100 Gamma = 0.67Gamma = 0.00 Low-income democrats support health care reform more than lower-income republicans do; high-income democrats and republicans show no relationship between party affiliation and support for health care reform.

Interpreting the controls Controlling for a third variable can help you understand the bivariate relationship you’re interested in Controlling for a third variable can help you understand the bivariate relationship you’re interested in Controlling for a third variable can tell you that the original relationship Controlling for a third variable can tell you that the original relationship Is spurious Is spurious Is maintained Is maintained Differs within categories of the 3rd variable Differs within categories of the 3rd variable

GSS data and 3-variable relationships May find spurious relationships May find spurious relationships More likely to find specified relationships More likely to find specified relationships Very likely to look at joint impact of two independent variables on a dependent variable Very likely to look at joint impact of two independent variables on a dependent variable

Example Hypothesis: People with more children will have more conservative or traditional views on childrearing. Hypothesis: People with more children will have more conservative or traditional views on childrearing. These views may differ by gender. These views may differ by gender.

Assignment 8 Control for third variable and interpret Control for third variable and interpret Find and summarize an article related to your topic Find and summarize an article related to your topic Briefly describe your projected research project. Briefly describe your projected research project.

Citations of Scholarly Articles Research-based papers very important Research-based papers very important In “Refereed” or Peer-reviewed journals In “Refereed” or Peer-reviewed journals Other sources (Newsweek, Washington Post, NYT, blogs, on-line informational sites) may be used as supplements, but be careful here. Blogs and wikpedia might be simply uninformed opinion. Do they belong in your paper? Other sources (Newsweek, Washington Post, NYT, blogs, on-line informational sites) may be used as supplements, but be careful here. Blogs and wikpedia might be simply uninformed opinion. Do they belong in your paper? Library data bases (e-journals) Library data bases (e-journals)

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