Statistics - Does smoking kill?

8/12/2019 Statistics - Does smoking kill?

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STAT 2

Lecture 3:

Does smoking kill?


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Review

The best way to test hypotheses isby carrying out experiments

Compare a treatment group to acontrol group; groups should be

identical except for the treatment Avoid confounding, bias


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Review

Ideally:

Use contemporaneous controls

andomise groups

!ouble blind


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Can we always do experiments?

"ypothesis: smo#ing causes lungcancer

Can$t force people to smo#e or notsmo#e

Can$t set up a control%o viable placebo


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Today

!oes smo#ing #ill&

'hy did it ta#e the scientific

community so long to decidewhether smo#ing was ha(ardous ornot&


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Today

!ifferent designs for observationalstudies

'hat advantages anddisadvantages do these differentdesigns have&


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I: Does smoking kill?


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Lung cancer

are disease before modern times

Incidence rose mar#edly in the

early )*thcentury Cigarette smo#ing became

fashionable in the late +th

century Could there be a connection&


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1912: Isaac Adler

-bserved lung cancer morecommon among men than women

.the irritations and traumatisms which must befre/uent in the more unprotected life of men0the abuse of tobacco and alcohol, the manytrades and vocations which are accompaniedby irritations of the respiratory organs, etc12111The entire sub3ect is not yet ready for final3udgment14


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192: Lom!ard and "oering

5uestioned )+6 cancer patientsand )+6 controls; controlled for

gender and age Cancer group: 768 heavy

smo#ers; control group: )*8heavy smo#ers

Cancer of lung9lip9chee#93aw: 7

out out heavy smo#ers


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192: Lom!ard and "oering


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19#$: %c&airer and %c&oniger

78 weresmo#ers

In lung cancer group, 68 were

smo#ers


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19': "oll and (ill

Interviewed lung cancer patientsnewly admitted to hospitals

Interviewed other randomlyselected hospital patients

Control CancerSmokers 1296 1350

Nonsmokers 61 7


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19#: "oll and (ill


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19): R*A* +is&er

Incipient cancer, or a pre@cancerous condition, may induce

smo#ing


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199#: ,raun- Caporaso- .age-(oover

xamined B>+ pairs of male twinswhere at least one died of lung

cancer After controlling for other factors,

identical twin of lung cancervictim no more li#ely to developlung cancer than fraternal twin


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199#: ,raun- Caporaso- .age-(oover

!oesn$t mean there no geneticeffect, only that it$s small

compared to other effects


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Cross/sectional studies

xamine a population data set =ight only have data on groups,

not individuals oo# at incidence of disease andpossible cause among differentgroups

elate disease and cause

fre/uencies


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-ften re/uire no new data

Can cover very large populations

"uge amounts of confounding

Impossible to determine cause and

effect


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Alcohol and heart disease

"eavy drin#ers have a higher

incidence of heart disease thannon@drin#ers

=oderate drin#ers have a lowerincidence of heart disease thannon@drin#ers


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Case/control studies

Consider a group of people whohave a certain condition

Also consider a group of peoplewho don$t have the condition

oo# for characteristics of the +st

group that are different from )nd

Can loo# at individual differences


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Dood for trac#ing rare events

Comparatively cheap and /uic#


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Seat Belt Studies

Case@control studies of road

accident victims seemed to show ahuge decrease in serious in3ury ifyou wore a seat beat


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Co&ort studies

Cohort:group of people who sharea common characteristic

Compare to a control cohort whodiffer in only one respect

=atch for gender, race, economicstatus, other health, etc1

Trac# groups for a long time


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Co&ort studies

=ost li#ely confounders can becontrolled for

Can almost isolate variable in/uestion

!oesn$t rule out uncontrolledconfounding factors

Eery difficult to establish causality


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Co&ort studies

Nurses' Health Study

!esigned to assess ris# factors for

cancer and heart disease "as trac#ed +)**** nurses since

+6B =any ma3or health findings have

followed


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%trengt& o0 evidence

+1 andomised experiments

)1 Unrandomised experiments

1 Cohort studies

71 Case@control studies

1 Cross@sectional studies

BF1 xpert opinion

%ote: exact ran#ing will depend on /uality of study


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Recap


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Recap

Cross@sectional studies loo# atincidences and possible cause at a

particular point in time Case@control studies loo# for

uncontrolled differences between acase group and a control group


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Recap

Cohort studies trac# two groupsthat differ in a certain respect over

an extended period of time Though none of these is as

definitive as a experiment, if weeliminate all other plausiblecauses, we can ma#e strong

statements


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ext time:

Turning numbersinto pictures

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Statistics - Does smoking kill?