4 Risk and Causation

8/16/2019 4 Risk and Causation

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RISK &CAUSATIONFRANCES AVILES

MD MPH BSC



COHORT STUDY

Cohort: group of pop! "ho #h$r $ %oo'%h$r$%tr(#t(%

I)'t(*# people with risk factors $')%op$r# )(#$# ('%()'% to ('%()'% r$t ('$'othr group of people without those riskfactors+

Connects Incidence to a Causality

L$rg S$p! S(,#

E-p'#(./T( Co'#u('g



COHORT STUDY: RISK FACTOR

E0POSURE

PROSPECTIVE: To"$r)# th futur1 fo!!o"# )(#$#('%()'% 2MC3

RETROSPECTIVE: Loo4# ('to p$#t $r%h(.) )$t$

Pro#p%t(. #tu)(# fo!!o" $ %ohort ('to th futurfor $ h$!th out%o+

Rtro#p%t(. #tu)(# tr$% th %ohort 5$%4 ('

t( for -po#ur ('for$t(o' $ftr th out%oh$# o%%urr)+ Rtro#p%t(. #tu)(# group#u56%t# 5$#) o' th(r -po#ur #t$tu# $')%op$r th(r ('%()'% of )(#$#+



Pro#p%t(. Cohort

I' $ Ho#p(t$! 7 A group of h$.8 #o4r# $') $group of 'o'9#o4r# $r #!%t) for $ %ohort

#tu)8+ Lu'g C$'%r ('%()'% (# $####) for thfo!!o"('g 8$r#+





Start

Exposure

? ? ? ? ? ? ? ? ? ?

Disease

Time



Cohort Stu)8

out%o (# $#ur) $ftr -po#ur

8(!)# tru ('%()'% r$t# $') r!$t(. r(#4#

$8 u'%o.r u'$'t(%(p$t) $##o%($t(o'# "(th out%o

5#t for %oo' out%o#

-p'#(.

r;u(r# !$rg 'u5r#

t$4# $ !o'g t( to %op!t

pro' to $ttr(t(o' 5($# 2%op'#$t 58 u#('g pr#o'9t( tho)#3

pro' to th 5($# of %h$'g (' tho)# o.r t(



CASE CONTROL STUDY:

DISEASE

U## $ group of people with disease $') $$t%h('g group of non-diseased pop!2CONTROL3

RETROSPECTIVE: Loo4# 5$%4 (' t( for thpr#'% or $5#'% of r(#4 f$%tor#+

Loo4# for %$u#$!(t8 of r(#4 f$%tor# 58 $'$!8,('gth pr#'% of r(#4 f$%tor# (' p$t('t# "(th g(.')(#$# $') th $5#'% of th# RF# (' th#!%t) p$t('t# th$t $r 'ot )(#$#)+





Start? ? ? ? ? ? ? ? ? ?

Disease

L! "#C!

Exposure



C$# Co'tro!

out%o (# $#ur) 5for -po#ur

%o'tro!# $r #!%t) o' th 5$#(# of 'ot h$.('gth out%o

goo) for r$r out%o#

r!$t(.!8 ('-p'#(.

#$!!r 'u5r# r;u(r)

;u(%4r to %op!t

pro' to #!%t(o' 5($#

pro' to r%$!!/rtro#p%t(. 5($#



R(#4& M$#ur't#of R(#4 $') E=%t



RISK

To $'$!8, $ Stu)8> R(#4 ')# to 5 $####)

$isk : th proport(o' of pr#o'# "ho $r u'$=%t)$t th 5g(''('g of $ #tu)8 pr(o)> 5ut "ho %ou!)po##(5!8 -pr('% $' .'t 2+g+> )$th> )(#$#>or ('6ur83 )ur('g th #tu)8 pr(o)

%uantifying $isk : R!$t(. r(#4> $ttr(5ut$5! r(#4>$') th o))# 2or o))# r(#43 r$t(o $r $#ur#u#) to ;u$'t(f8 r(#4 (' popu!$t(o' #tu)(#



The knowledge that something is a risk factor

for a disease can be used to help: ? Pr.'t th )(#$#+

? Pr)(%t (t# futur ('%()'% $') pr.$!'%+

? D($g'o# (t 2)($g'o#t(% #u#p(%(o'# $r h(ghr (f (t (#4'o"' th$t $ p$t('t "$# -po#) to th r(#4 f$%tor3+

? E#t$5!(#h th %$u# of $ )(#$# of u'4'o"'t(o!og8+



A5#o!ut R(#4

Th fu')$'t$! $#ur of r(#4 (#

('%()'%+ Th ('%()'% of $ )(#$# (#> ('f$%t> th $5#o!ut r(#4 of %o'tr$%t('g (t+

If th INCIDENCE of )(#$# (# @ pr @> pop! pr Yr+

Th' th ABSOLUTE RISK of $ pr#o' $%tu$!!8 %o'tr$%t('g (t(# $!#o @ pr @> pr Yr+> or @ pr Yr+



M$#ur# of RISK & EFFECT

M$#ur# of =%t to 5('g -po#) to $ r(#4 f$%tor o' thr(#4 of %o'tr$%t('g $ )(#$#+

A 'u5r of )(=r't %op$r(#o'# of r(#4 %$' 5 $)>('%!u)('g relati&e risk > attri'uta'le risk > $') th oddsratio+





R!$t(. R(#4 2RR3

RELATIVE RISK : (# th group or or !## !(4!8 to ).!opD)

*$$+ I,CIDE,CE I, E.SED/I,CIDE,CE I,0,E.SED1

For -$p!> th ('%()'% r$t of !u'g %$'%r $o'g #o4r# ('

N" r#8 (# 23/4333> "h(! th ('%()'% r$t of !u'g %$'%r$o'g 'o'#o4r# (' N" r#8 (# 2/4333+

Thrfor> th %h$'% of gtt('g !u'g %$'%r 2th r!$t(. r(#43 for th(#N" r#8 popu!$t(o' (#



RELATIVE RISK REDUCTION

Th proport(o' of r(#4 r)u%t(o' $ttr(5ut$5! to th ('tr.'t(o' $#%op$r) to $ %o'tro!+

$$$+ 4 - relati&e risk

$$$+ #$/I5

I5+ highest incident rate

IL+ lowest incident rate

Rport# of r(#4 r)u%t(o'# )u to tr$t't# (' $'8 %!('(%$! tr($!#> $') ('$!o#t $!! ph$r$%ut(%$! $).rt(#'t#> $r of relati&e risk reductions



Thr "r )$th# fro %$r)(o.$#%u!$r %$u## (' th p!$%5ogroup 2G '31 th %$r)(o.$#%u!$r ort$!(t8 r$t "$#thrfor />G +GG 226273 (' th(# group+

I' th pr$.$#t$t(' group 2>G '3> thr "r %$r)(o.$#%u!$r )$th#> g(.('g $ ort$!(t8 r$t of />G +@> or 4687+

Th $$ of )$th (' tho# g(.' th )rug (# @+/G+G +J>

Th $$$ (# 2@ 9 +J3+G> or G #ho"('g th$t $' (pr##(.G of %$r)(o.$#%u!$r )$th# "r pr.'t) 58 th )rug+

Th #$$ (# 2G+G 9 @+3 + $ f$r !## (pr##(.9#ou')('g *gur> #ho"('g th$t of $!! ' g(.' th )rug for +8$r#> + of th "r #$.) fro $ %$r)(o.$#%u!$r )$th+



ATTRIBUTABLE RISK 2AR3

Th $))(t(o'$! ('%()'% of $ )(#$# th$t (# $ttr(5ut$5! to th r(#4f$%tor (' ;u#t(o'+ Th )(=r'% (' r(#4 5t"' -po#) $')

u'-po#) group#> or th proport(o' of )(#$# o%%urr'%# th$t $r$ttr(5ut$5! to th E-po#ur

ATTRIBUTABLE RISK: ho" $'8 or %$##

*#$+ I,CIDE,CE $#TE I, E.SED-I,CIDE,CE $#TE I, 0,E.SED1

Th'> th r(#4 of !u'g %$'%r $ttr(5ut$5! to #o4('g 2th $ttr(5ut$5! r(#43 (' th(# N" r#8 popu!$t(o' (# G/@ ('u# G/@ or @/@+



G0G T$5!

a '

c d

$IS! E.S0$E

0,E.SED

D) , D) TT#L

a9'

c9d

Ho" $'8 "r -po#)

Ho" $'8 "r 'ot -po#)

Ho" $'8h$. )(#$#

Ho" $'8 )o 'oth$. )(#$#

:Incidence in Exposed; a/a9'

:Incidence in 0nexposed; c/c9d



Attr(5ut$5! R(#4 $') R!$t(. R(#4 $r $('!8u#) for Cohort# Stu)(#

O))# R$t(o $r %oo'!8 u#) for C$# Co'tro!Stu)(#



Attr(5ut$5! R(#4 R)u%t(o'

Th )(=r'% (' r(#4 $ttr(5ut$5! to th('tr.'t(o' $# %op$r) to %o'tro!

R(#4 of ('tr.'t(o' group 7 R(#4 of Co'tro! <roup



#'solute Di<erence of $isk

$isk di<erence (# th r(#4 (' th -po#) group('u# th r(#4 (' th u'-po#) group+

•If $' -po#ur (# h$rfu! 2$# (' th %$# of

%(g$rtt #o4('g3> th r(#4 )(=r'% (#-p%t) to 5 gr$tr th$' +

•If $' -po#ur (# prot%t(. 2$# (' th %$# of $.$%%('3> th r(#4 )(=r'% (# -p%t) to 5

!## th$' +

•R(#4 )(=r'% (# $!#o 4'o"' $# attributable risk +

$ate di<erence 2$5#o!ut )(=r'% (' r$t3 (#

th r$t (' th -po#) group ('u# th r$t ('



ATTRIBUTABLE RISK PERCENT

Pr%'t of %$## )u to -po#ur

U#) to $#### proport(o' of %$##)u to r(#4 f$%tor+

AR RR9@/RR



NUMBER NEEDED TO TREAT: NNT

NUMBER NEEDED TO HARM: NNH

PREVENTION: NNT

CAUSALITY: NNH Ho" $'8 h$. to )o #oth('g to pr.'t o'

%$# of )(#$#

Ho" $'8 "ou!) h$. to #top #o4('g 9 NNT

Ho" $'8 pt# "ou!) h$. to #o4 9 NNH



Nu5r ')) to Tr$t

Nu5r of p$t('t# "ho ') to 5 tr$t) for @p$t('t to 5'*t+

,,T+4/#$$6



Nu5r ')) to H$r

Nu5r of p$t('t# "ho ') to 5 -po#) to $r(#4 f$%tor for @ p$t('t to 5 h$r)+

,,5+4/#$



ODDS RATIO

ODDS RATIO: E#t($t# th ('%r$#) o))# of h$.('gr(#4 f$%tor# "h' %op$r('g )(#$# $') 'o'9)(#$#)group#

*$+ad/'c1 Not $ pr)(%t(o' of )(#$#

E#t($t# th#tr'gth of r(#4 f$%tor#+

S('% ('%()'% )$t$ $r 'ot $.$(!$5! (' $ %$#9%o'tro! #tu)8> th o))# r$t(o %$' 5u#) $# $' #t($t of r!$t(. r(#4 "h' $ disease is uncommon

a '

c d



• Of G p$t('t# (' th ho#p(t$!> h$. !u'g %$'%r+ Ofth# p$t('t#> $r #o4r#+

• Of th r$('('g @ ho#p(t$!(,) p$t('t# "ho )o 'oth$. !u'g %$'%r> J $r #o4r#+

• U# th(# ('for$t(o' to %$!%u!$t th o))# r$t(o for#o4('g $') th r(#4 of !u'g %$'%r+

.eople with lung cancer A B

.eople without lung cancer C J D

2A32D3 2323 / 2B32C3 232J3

/ OR@+

• A' o))# r$t(o of @+ $'# th$t th r(#4 of !u'g %$'%r (#

@+ t(# h(ghr (' pop!"ho #o4 th$' (' tho# "ho)o 'ot #o4+



CAUSATION



CONCEPT OF CAUSE• A' u')r#t$')('g of th %$u## of )(#$# (#

(port$'t (' th h$!th *!) 'ot o'!8 for

pr.'t(o' 5ut $!#o (' )($g'o#(# $') th$pp!(%$t(o' of tr$t't+

• A cause of $ )(#$# (# $' .'t> %o')(t(o'>%h$r$%tr(#t(%> or %o5('$t(o' of th# f$%tor#

"h(%h p!$8# $' (port$'t ro! (' pro)u%('g th)(#$#+

• A %$u# %ou!) 5 sufcient or necessary



SUFFICIENT CAUSE• A %$u# (# tr) #u%('t "h' (t

('.(t$5!8/%rt$('!8 pro)u%# or ('(t($t# $ )(#$#+

•

It (# 'ot u#u$!!8 $ #('g! f$%tor> 5ut oft' %opr(###.r$! %opo''t#+ +g+ %(g$rtt #o4('g (# o'%opo''t of th #u%('t %$u# (' !u'g %$'%r+

• I' g'r$!> (t (# 'ot '%##$r8 to ()'t(f8 $!! th%opo''t# of $ #u%('t %$u# 5for =%t(.

pr.'t(o' %$' t$4 p!$%> #('% th ro.$! ofo' %opo''t $8 ('trfr "(th th $%t(o' ofth othr# $') thu# pr.'t th )(#$#+



NECESSARY CAUSE

• A %$u# (# tr) '%##$r8 (f $ )(#$#%$''ot ).!op (' (t# $5#'%+

• E$%h #u%('t %$u# h$# $ '%##$r8 %$u#$# $ %opo''t+



Types of Causes

• Su=cient 9 If th %$u# (# pr#'t> )(#$# "(!!$!"$8# o%%ur+

• ,ecessary 9 Th %$u# u#t 5 pr#'t for th)(#$#/%o')(t(o' to o%%ur> $!though (t )o# 'ot

$!"$8# r#u!t (' )(#$# 2'ot '%##$r(!8#u%('t3

• $isk factor 9 I'%r$## th pro5$5(!(t8 of $

p$rt(%u!$r )(#$#/%o')(t(o' (' $ group of pop!%op$r) "(th $' othr"(# #((!$r group ofpop! "ho !$%4 th(# f$%tor 2'(thr '%##$r8'or #u%('t3



>aria'le #ssociations



>aria'le #ssociations Example@



idirectional Causality



"idirectionalCausality

$ate and $isk



$ate and $isk

•A rate (# $ goo) $ppro-($t(o' of r(#4 (f th:• E.'t (' th 'ur$tor o%%ur# o'!8 o'%

pr (')(.()u$! )ur('g th #tu)8 ('tr.$!• Proport(o' of th popu!$t(o' $=%t) 58 th

.'t (# #$!! 2+g+> !## th$' 3• T( ('tr.$! (# r!$t(.!8 #hort

•If th .'t (' th 'ur$tor o%%ur# orth$' o'% )ur('g th #tu)8 2+g+> %o!)#> $r('f%t(o'#> $#th$ $tt$%4#3 $ r!$t) #t$t(#t(%%$!!) incidence density #hou!) 5 u#)('#t$) of r$t

eps n e erm n ng ause



eps n e erm n ng auseand E<ect

@+I'.#t(g$t(o' of th #t$t(#t(%$! $##o%($t(o'

2Mill’s Canons3@+Str'gth of $##o%($t(o'G+Co'#(#t'%8+Sp%(*%(t8

+B(o!og(%$! p!$u#(5(!(t8+Do# r#po'#

G+I'.#t(g$t(o' of th tpor$! r!$t(o'#h(p•.L$t't pr(o)# $4 o'#t of r(#4 f$%tor#

u'%!$r

+E!(('$t(o' of $!tr'$t(. -p!$'$t(o'#•.Never !(('$t) fu!!8 or (')*'(t!81

%h$!!'g) 58 $%h '" -p!$'$t(o' th$t *t#

th )$t$



nly A .ossi'ilities for #ny

#ssociation

@+C$u#$! 2tru $##o%($t(o'3G+Ch$'% 25$#) o' pro5$5(!(t83+R$')o rror 2'o'9)(=r't($! rror3+S8#t$t(% rror 25($#3

• Co'fou')('g 2#p%($! %$# of 5($#3



Specific Types of Rates









@3 K$t, D> t $!+ 4!# Ep()(o!og8> B(o#t$t(#t(%#> Pr.'t(. M)(%('>$') Pu5!(% H$!th+ th E)+ S$u')r#: Ph(!$)!ph($> PA+ G@+

G3 D$ughrt8 S> t $!+ USMLE> Stp @> Bh$.(or$! S%('%> Ep()(o!og8> &B(o#t$t(#t(%#+ B%4r Prof##(o'$! E)u%$t(o'+ G@+

3 Bro"' T> Sh$h S+ B(o#t$t(#t(%#+ USMLE STEP @ SECRETS+ r) E)+S$u')r#: Ph(!$)!ph($> PA+ G@+

3 Pr('%(p!# of Ep()(o!og8 (' Pu5!(% H$!th Pr$%t(%: A' I'tro)u%t(o' toApp!() Ep()(o!og8 $') B(o#t$t(#t(%#+ C'tr# for D(#$# Co'tro! $')

Pr.'t(o'+ Th(r) E)(t(o'+ Pu5!(#h) GJ+ Up)$t) G@@+ http://"""+%)%+go./oph##/%#!#/)#p)/##@/(')-+ht!

3 L T> t $!+ F(r#t A() for th USMLE Stp @> $ Stu)'t to Stu)'t<u()+ M%<r$" H(!! E)u%$t(o'+ G@+

J3 <!$#r A+ H(gh Y(!) B(o#t$t(#t(%#> Ep()(o!og8> $') Pu5!(% H$!th+L(pp('%ott (!!($# $') (!4('#1 th E)+ G@+ Ch +

REFERENCES

http://www.cdc.gov/ophss/csels/dsepd/ss1978/index.html




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