8/12/2019 Health and Societ2

1/7

Health and Society

Socioeconomic status is one of the fundamental driversof population health.

socioeconomic gradient in health totanic case

Class Saved Total

First 203 325

Second 118 285

Third 178 706

Crew 212 885

This differential patterning of survival is what we call thesocioeconomic gradient in

health.

Why was there a social class gradient in

8/12/2019 Health and Societ2

2/7

mortality on the Titanic?

Confounding by age and sex of passengers in different sections of the boat.

Age, sex

Class Survival

Mortality on board Titanic, by gender

and class

Class Men Women/Children

First 67.4% 2.7%

Second 91.7% 11.2%

Third 83.8% 57.8%

Why was there a social class gradient in mortality on the Titanic?

1. Confounding by age and sex of passengers in different sections of

the boat.

2. Upper class people were physically more fit, or quicker to respond

to instructions of the crew.

3. Discrimination against 3rd class passengers / Preferential treatment

of 1st class passengers.

4. Structural differences in access to life-saving resources (lifeboats).

1. However, probably the most compelling and parsimonious reason for the

2. socioeconomic gradient is that they were structural differences in access

3. to lifesaving technology--

4. in this case, access to the lifeboats on board the Titanic--

5. according to whether you were first, second, or third class.

6. We can see this from a diagram of the cross section of the boat at the

7. moment it struck the iceberg.

Evidence of SES gradients in health in contemporary society

Income

8/12/2019 Health and Societ2

3/7

Educational attainment

Occupation

In studying the association between education and health, a pre-existing

health condition that affects ones educational attainment is an example of

reverse causation (i.e., health predicted SES attainment).

An SES gradient in health has been observed for outcomes such as mortality

and chronic disease mortality by measures such as income, education, and

occupation.

8/12/2019 Health and Societ2

4/7

Two types of threat to causal inference

Reverse Causation

Bad health compromises educational attainment, not the other way round

It is often asserted that education is less susceptible to reverse causation

(compared to income & occupation)

Most people have completed their schooling by the time they develop chronic

disease

If you get sick, you cant lose education (in the way that you can lose income or

your job)

But is that strictly accurate?

How we tease eduation and health

A birth cohort is basically a kind of longitudinal followup study in which we

take a large number of babies who were just born, and then follow themup over a

lifetime to see which came first, theillnesses or their schooling.

In short, chronic conditions during childhood e.g. diabetes, ADHD, or mental

health problems result in children missing school

Reverse causation is real!

Though not every instance of SES gradients reflects this bias(tendency)

health doesn't mean that all of that was because lack of schooling led to bad

health.

Some part of that correlation is likely to be driven by the reverse--that is, bad

health leads to truncated education.

Brians health status influenced his choice of occupation (and potentially his

income); therefore, this scenario best represents reverse causation(i.e., health

influenced SES attainment).

8/12/2019 Health and Societ2

5/7

Confounding1(omitted variable bias)

Association between SES & health is spurious, and reflects the influence of omitted

third variables.

if you want to check whether that relationship is confounded, then you would want

to repeat the analysis by breaking up the sample into smokers versus nonsmokers.

This is the principle of stratification.

among smokers, there's no additional risk of lung cancer from carrying matches in

your pocket.

If you're a non-smoker, it does not increase your risk of lung cancer by carrying

matches around in your pocket.

ergo, cigarette smoking is a confounder of the association between carrying

matches and getting lung cancer.

1En una investigacin cientfica, una variable de confusino factor de confusines

unavariableo factor que distorsiona la medida de la asociacin entre otras dos variables.

http://es.wikipedia.org/wiki/Variable_(matem%C3%A1ticas)http://es.wikipedia.org/wiki/Variable_(matem%C3%A1ticas)http://es.wikipedia.org/wiki/Variable_(matem%C3%A1ticas)http://es.wikipedia.org/wiki/Variable_(matem%C3%A1ticas)

8/12/2019 Health and Societ2

6/7

As I've showed it here, it's cigarette smoking which is the cause of carrying

matches, and moreover, there is no relationship between carrying matches and

getting lung cancer. That's the true nature of the association between the three

variables, which I have shown in this diagram.

An investigator is interested in studying differential cancer incidence

rates between subpopulations based on certain characteristics (i.e.,

race/ethnicity, insurance status, gender) in the United States. However,

she is concerned that socioeconomic status (SES) might confound the

relationship between the exposure (subpopulation characteristic) and

the outcome(incidence of cancer), where X Y. In which of the

following scenarios, should she be concerned about potential

confounding by SES?

A confounder is a variable that precedes the exposure and outcome of

interest, AND is independently associated with the exposure and

outcome of interest. SES does not cause gender or race. However,

gender and/or race can affect SES. Therefore

SES would not be a confounder in those situations. However, SES can

precede and affect insurance status. Therefore, SES may be a

confounder in this scenario.

Maria is a toddler who demonstrates high ability to delay gratification.

As an elementary school student, she performs well academically and

exhibits self-regulation over her health behaviors, including consuming

less fast food compared to her classmates. She is enrolled in a

longitudinal study examining the effects of education on health. In this

study, Marias ability to delay gratification is an example of which of thefollowing?

8/12/2019 Health and Societ2

7/7

The ability to delay gratification is an example of confounding in this

case because previous studies indicate that this ability is independently

associated with educational performance and with self-regulation of

behaviors, and this ability (observed during her early childhood years)

preceded Marias educational performance during elementary school.