max 201 quantitative methods for the social sciences controlling for a third variable; developing a...
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MAX 201MAX 201Quantitative Methods for Quantitative Methods for
the Social Sciencesthe Social Sciences
Controlling for a Third Controlling for a Third Variable;Variable;
Developing a Research TopicDeveloping a Research Topic
Univariate, bivariate, and Univariate, bivariate, and multivariate analysismultivariate analysis
Most basic data descriptionMost basic data description: statistics : statistics applied to one variable: mean, median, applied to one variable: mean, median, percentages.percentages.
Bivariate analysisBivariate analysis uses contingency uses contingency tables to look at two variables at a time.tables to look at two variables at a time.
Introducing a Introducing a third variablethird variable is called is called controlling or specifying the original controlling or specifying the original relationship.relationship.
Controlling for a third Controlling for a third variable: sex and auto variable: sex and auto
accidentsaccidents Men have more accidents than women Men have more accidents than women
(gender is related to accident involvement)(gender is related to accident involvement) Introduce a third variable: miles driven per Introduce a third variable: miles driven per
yearyear Gender is related to miles driven (men drive Gender is related to miles driven (men drive
more)more) Miles driven is related to accidents (the more Miles driven is related to accidents (the more
you drive, the more likely you are to have an you drive, the more likely you are to have an accident).accident).
Sex & accidents: spurious Sex & accidents: spurious relationshiprelationship
SEXSEX
ACCIDENT ACCIDENT FrequencyFrequency
MILES drivenMILES driven
SEXSEX
ACCIDENT FrequencyACCIDENT Frequency
Control Variable as an Control Variable as an Intervening Variable Intervening Variable
Ind.
Var.ControlVariable
Dep.Var.
Caffeine and Heart AttacksCaffeine and Heart Attacks One study linked caffeine consumption with an One study linked caffeine consumption with an
increased of heart disease. increased of heart disease. Study did not control for a third variable: Study did not control for a third variable:
whether patients in the smoked.whether patients in the smoked. Heavy caffeine consumers also smoke.Heavy caffeine consumers also smoke. Further study revealed that smoking not Further study revealed that smoking not
caffeine was the cause of the heart disease.caffeine was the cause of the heart disease. Source: Ian Ayres, Super Crunchers. NY: Source: Ian Ayres, Super Crunchers. NY:
Bantam: 2007: pp 90-91. Bantam: 2007: pp 90-91.
Wealthier is HealthierWealthier is Healthier For countries, a graph of mortality For countries, a graph of mortality
against income reveals that against income reveals that populations of richer countries live populations of richer countries live longer. longer.
For individuals within a country, For individuals within a country, higher- income individuals live longer higher- income individuals live longer than lower-income individuals. than lower-income individuals.
The relationships are much more The relationships are much more complex, however. complex, however.
Wealthier is HealthierWealthier is Healthier
For countries, public health –sanitation and removal For countries, public health –sanitation and removal of waste – plays an important role. Big Medicine – of waste – plays an important role. Big Medicine – vaccination and antibiotics – play a role. Individual vaccination and antibiotics – play a role. Individual care plays a larger role as income grows. care plays a larger role as income grows.
In poor countries, mosquitoes, AIDS, unsafe drinking In poor countries, mosquitoes, AIDS, unsafe drinking water and other public health issues play a large water and other public health issues play a large role in mortality. role in mortality.
Insecticide will work to some degree on mosquitoes, Insecticide will work to some degree on mosquitoes, but eventually mosquitoes develop a resistance. but eventually mosquitoes develop a resistance. Need to remove open, stagnant pools where Need to remove open, stagnant pools where mosquitoes breed. mosquitoes breed.
Wealthier is HealthierWealthier is Healthier
For individuals, the relationship between For individuals, the relationship between health and income is more complex. health and income is more complex.
Better utilization of knowledge about Better utilization of knowledge about health (smoking) and more education may health (smoking) and more education may cause health, rather than income directly cause health, rather than income directly causing health. causing health.
Certain groups experience more stress Certain groups experience more stress from discrimination, low-income and that from discrimination, low-income and that harms health. harms health.
Source: David Cutler, Angus Deaton, Adriana Lleras-Muney. “”The Source: David Cutler, Angus Deaton, Adriana Lleras-Muney. “”The Determinants of Mortality.” Journal of Economic Perspectives. 20 Determinants of Mortality.” Journal of Economic Perspectives. 20 (3) 2006: 97-120.(3) 2006: 97-120.
Controlling for a third Controlling for a third variable: health care and variable: health care and
party idparty id Controlling for a third variable Controlling for a third variable
discussed in the chapter from the Cole discussed in the chapter from the Cole book, “Sorting Out Relationships”book, “Sorting Out Relationships”
Work through that example:Work through that example: original relationship is support of health original relationship is support of health
care and party identification (10.1)care and party identification (10.1) control variable is income control variable is income different possibilities are considereddifferent possibilities are considered
Party ID and Health Care ReformParty ID and Health Care Reform
Support Health Care Reform
Republican Democrat Totals
No 73 37 110
Yes 67 123 190
Totals 140 167 300
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 ReformParty ID and Health Care ReformIncome: Low Income: High
Support Health Care
R D Totals R D Totals
No 33 27 60 40 10 50
Yes 27 113 140 40 10 50
Totals 60 140 200 80 20 100
Gamma = 0.67 Gamma = 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 controlsInterpreting the controls Controlling for a third variable can help Controlling for a third variable can help
you understand the bivariate you understand the bivariate relationship you’re interested inrelationship you’re interested in
Controlling for a third variable can tell Controlling for a third variable can tell you that the original relationshipyou that the original relationship Is spuriousIs spurious Is maintainedIs maintained Differs within categories of the 3rd variableDiffers within categories of the 3rd variable
GSS data and 3-variable GSS data and 3-variable relationshipsrelationships
May find spurious relationshipsMay find spurious relationships More likely to find specified More likely to find specified
relationshipsrelationships Very likely to look at Very likely to look at joint impactjoint impact of of
two independent variables on a two independent variables on a dependent variabledependent variable
ExampleExample
Hypothesis: People with more Hypothesis: People with more children will have more conservative children will have more conservative or traditional views on childrearing.or traditional views on childrearing.
These views may differ by gender.These views may differ by gender.
# of children * Child Suffers if Mom Works Crosstabulation
294 315 609
48.3% 51.7% 100.0%
147 108 255
57.6% 42.4% 100.0%
441 423 864
51.0% 49.0% 100.0%
0-2
3 or more
# of children
Total
Agree Disagree
Child Suffers if MomWorks
Total
RESPONDENTS SEX * Child Suffers if Mom Works Crosstabulation
218 146 364
59.9% 40.1% 100.0%
224 277 501
44.7% 55.3% 100.0%
442 423 865
51.1% 48.9% 100.0%
MALE
FEMALE
RESPONDENTSSEX
Total
Agree Disagree
Child Suffers if MomWorks
Total
# of children * Child Suffers if Mom Works * RESPONDENTS SEXCrosstabulation
158 113 271
58.3% 41.7% 100.0%
59 33 92
64.1% 35.9% 100.0%
217 146 363
59.8% 40.2% 100.0%
136 202 338
40.2% 59.8% 100.0%
88 75 163
54.0% 46.0% 100.0%
224 277 501
44.7% 55.3% 100.0%
0-2
3 or more
# of children
Total
0-2
3 or more
# of children
Total
MALE
FEMALE
Agree Disagree
Child Suffers if MomWorks
Total
Assignment 8Assignment 8
Control for third Control for third variable and variable and interpretinterpret
Find and summarize Find and summarize an article related to an article related to your topicyour topic
Briefly describe Briefly describe your projected your projected research project. research project.
Citations of Scholarly Citations of Scholarly ArticlesArticles
Research-based papers very important Research-based papers very important In “Refereed” or Peer-reviewed journalsIn “Refereed” or Peer-reviewed journals Other sources (Newsweek, Washington Other sources (Newsweek, Washington
Post, NYT, blogs, on-line informational Post, NYT, blogs, on-line informational sites) may be used as supplements, but be sites) may be used as supplements, but be careful here. Blogs and wikpedia might be careful here. Blogs and wikpedia might be simply uninformed opinion. Do they simply uninformed opinion. Do they belong in your paper?belong in your paper?
Library data bases (e-journals) Library data bases (e-journals)
top related