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nbme24/Block 4/Question#30 (58.3 difficulty score)
An investigator is studying an outbreak of ...
Only cookies are independently associated with E. coli casesπŸ”

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submitted by niboonsh(336),
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thsi isuonteq sekam me tnaw to aet na e ilco oioekc adn phoe i lebed uot

caitlyncloy  pick C and move on was my strategy :P help lol +1  
thegooddoctor2  lol good one +1  

submitted by doodimoodi(55),
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iDd on neo tcinoe htat het ddsO riota on teh top etfl si onw?gr Am I imigsns ?ehontigms If oyu utlecaalc it, t'is 6 sjut ekli het otp ghrti

mjmejora  thats actually really funny +  
yex  Because I said so, applies here... :-/ +1  
doodimoodi  Cant believe we pay $60 for this crap +36  
aisel1787  best comment doodimoodi) +1  
b1ackcoffee  that fucking threw me off on exam. I was like is there an effect modification by "Not drinking milk". the fuck! +  

submitted by sne(45),
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RO ;tg&1 necdsaiti riseadecn ueorccencr of The lony RO rteegar nhat 1 wsa ni hte tbael atth itnacdeid hatt hte jcsuteb ate eoskcio tbu dti'nd kindr lmi.k uTs,h ahtt is the yonl eon itwh a ifnaiicgnts noercceruc

For a more systematic approach. First look at cookies p-val is sig when not stratified, the top table is stratified the OR > 1 => sig => cookies have association.

Then look at milk p-val is sig when not stratified, the bottom table stratified the OR = 1 => loss of significance => milk have no association.

+/- peqmd(39),

Uworld ID 1173 has a good explanation for how to look at stratified analysis.

+/- peqmd(39),

submitted by pg32(140),
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The afct ttah eth dsdo aiotr ni the top flet is ciertorcn aesmk ihst sotnuiqe yrve ifudcilf.t It ksame ti paerpa sa fi the ocsekio rea sevucaita btu the lkmi hda eoms tipceeovtr atc.orf So .nooxsibou

drpatinoire  God I thought totally the same way as you did. I stared at this question for at least 5min and asked myself what's wrong with my statistics. +1  

submitted by youssefa(123),
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liItlinya mkil irnknidg saw dsaeaitcso hitw .ioclE otkubrae twhi =OR39. nad P1l0;t&0.0 rAfet inactriastofti ntio eta icokose adn did not aet eookcsi RO eacmeb 1 adetnsi of 3.9 gnaimen het onassoitica seeapi.adrdp erhferT,eo gaeitn oecokis asw a ufenrdonoc nda rhete is on rlea itsicasonao weeetbn drigiknn iklm adn,. sklim' te(h uofn)rdneco uinttobiocrn wsa ilssroenebp rof eth OR of 39. in het fsrit pa.lec This wsa ftrduheer tdemraednsto iwth OR of 6 ni eth oosecki anleo pg.our

submitted by qiss(12),

For people who generally had trouble reading the two charts:

First chart: We separated the entire population into two smaller populations to test for the cookies affect. In Population A (drank milk) there was an odds ratio of 6 (typo in the actual chart). In Population B (did not drink milk) there was an odds ratio of 6. Since the odds ratios are not 1, we can conclude that the cookies have an effect regardless of the population (ie drank milk people versus didn't drink milk people).

Second chart: New set of populations to test for the effect of milk. In Population C (ate cookies) there was an odds ratio of 1. In Population D (did not eat cookies) there was also an odds ratio of 1. This means that milk did not have an effect ever and didn't contribute to the disease.

"Only cookies are independently associated with E. coli cases" means that only the cookies cause the disease without the effects of something else.

submitted by sattanki(68),
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isTh one heter erwe rofu ddso i,otars one reiovdpd nrude ahec The ylon one ahtt ahd na dods iatro grtraee hnta 10. was the ltbea ni teh top hitgr (dsdO atoiR = 6, I ivee,l)eb iwhch hwne uyo kooled ta het alle,bs dle to het hrgit awenr.s

submitted by famylife(86),
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n"A dods aorti of 1 etsndciia htat eth dctioonni or eentv dnreu udtsy is leqyaul kilyel ot ocurc ni tbho og.spur An sdod itoar aegetrr tanh 1 cienidast tath the idniconot or envet si eomr lileky to ocrcu ni eht frtis roug"p. (kihrsit.pgdwkip/nitdoe:/sora_iiaew.t/dO/)

submitted by xw1984(4),

The OR in the upper left 22 table is incorrect, which should be 6 (726/36*2 =6), not 1. This means the OR of "ate cookies" does not change after stratification by "drank milk", so "drank milk" is not a confounder, and "ate cookies" is independently asso w/ EHEC outbreak.

On the other hand, OR for "drank milk" changed a lot (from 3.9 to 1.0), which indicates "drank milk" might be a confounder and, therefore, is not independently asso w/ EHEc outbreak.

submitted by tyrionwill(15),

we can make things simple like this way: if we want to know whether X1,or X2 correlates Y, we just separately test X1 and Y, and X2 and Y accordingly. When test X1 with Y, we require no X2 exposure; When test X2 with Y, we require no X1 exposure;

We test cookie with diarrhea, when milk was not drunk (top right): positive We test milk with diarrhea, when no cookie was eaten (lower right): negative

conclusion: only cookie correlates to the diarrhea

submitted by lilmonkey(18),
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Teh kdoeyrw si TEoNYssPDN)"Eaca"Dd(tNEIiLe. chiWh ni huanm gleaaugn mnsae "TNO "SIASAD.TEOC

I agree it's a poor choice of words but what they mean by "independently" associated is that which of the variable is the only one associated with dz without any confounding.

+/- peqmd(39),