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NBME 21 Answers

nbme21/Block 3/Question#21 (51.2 difficulty score)
A screening program is instituted for ...

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submitted by drdoom(896),
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02,05 enussttd ... btu oyu ifdn out iudngr rouy laitiin ercsen ttha 500 rdaealy aevh the ed.sesia ,oS etkutorsi htsoe epep.lo aTth evesla 002,0 tsudents hwo ’ndto veah eth eaised.s

verO eht roecus fo 1 er,ya you rcevisdo 020 stetduns vpeeodlde the fiionent.c suTh:

002 wne sasec / 00,02 peleop who nit’dd eahv the idseaes hewn uoy stetrda your dtysu = 10 ertpnec

T,cykri kytcri BENM ...

sympathetikey  Ah, I see. Thank you! +  
niboonsh  Im mad at how simple this question actually is +7  
sahusema  Incidence is measured from those AT RISK. People with the disease are not considered to be at risk. So 2500 - 500 = 2000 people at-risk. Of those 2000, within one year 200 develop the disease. So 200/2000 of the at-risk population develop the disease. 20/2000 = 10% = incidence +3  
daddyusmle  fuck im retarded +2  

submitted by drdoom(896),
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ontD’ grteof that iincndcee si het nbreum of wne eascs hwchi eegrem ni an eetfdncafu ppnuaiootl. cnedinceI is irnygt to get at het siuqntoe &g;t- nI“ a inevg ,yera hwo nmya wen elpoep peovled htis s?id”esea

In reoht ,drwos uoy tnaonc uonct eppeol hwo aldyera vaeh het dasiese. oYu ahve to xleucde tsoeh opleep rmof uyor ll.aoaunctci uYo twna ot ,kwon mnoga lla het ploepe tuo heret ohw OD TON ehva het ,ssediea woh ynam etmsi this aeyr swa oesnmeo ey(w)ln adgds?oein

Sdai nffirtydeel ,still uoy dot’n wtna ot bu”cld-oenuto“ pepoel hwo pdleveedo the esedsai febore ryou u.ysdt sA an iseli,imedgoopt atht wdluo wesrc up ruyo nsese fo how vietcfeni or tlnsmbairiess a eieadss s.i Yuo tawn to n,wko from“ eimt1 ot itme2 how mnya wen seacs meee?d”rg

questioneverything  You would count the total risk pool. Chlamydia is not a chronic disease so you would treat those 500 people and they would return to the risk pool. +1  
drdoom  But you would first have to determine that they CLEARED the infection. What if you gave them tx and then they come back and say, "doc i got the chlamydia" -- is this a new case or did the tx fail? You're assuming it cleared but maybe it didn't. That's why you want to EXCLUDE from the start anyone who might already have disease of interest. +7  

submitted by questioneverything(4),
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Ok I egt htat if 005 raladye heva teh eeidsas tenh the irsk oolp is eddprpo to 0002 ntstsdue utb hte ntqoesiu ciiclsyefpla assy ttha teh sett is onde a ryae lfr.tia..e 050 eelpop adh cih,ldyama you wluod arett uoY ton'd mecoeb iumenm ot mdyalhcia ratfe nfinoitce so tyeh uoldw go cakb noit eth ksri loo,p nnmgaie het lpoo owudl erunrt to 502.0 ehT wserna dlshou eb 8%, htis aws a dba .tsoiqeun

thepacksurvives  Yeah, this was my issue. I got it wrong because of this-- still don't understand the logic bc you can get chlamydia multiple times +6  
hungrybox  FUCK you're right. Damn I didn't even think about that. That's fucking dumb. I guess this is why nobody gets perfect scores on this exam lol. Once you get smart enough, the errors in the questions start tripping you up. Lucky for me I'm lightyears behind that stage lmao +9  
usmile1  to make it even more poorly written, it says they are doing a screening program for FIRST YEAR women college students. So one year later, are they following this same group of students, or would they be screening the incoming first years? +5  
dashou19  I think the same at first, but after a second read, the question stem said "additional" 200 students, which means the first 500 students don't count. +  
santal  @hungrybox You are me. +2  
neovanilla  @usmile1 I was thinking the exact same thing... +1  
happyhib_  I agree this is a trash question; I was like well if this is done yearly for new freshman the following year would be of the new class (but the word additional made me go against this). Also you could assume that they were treated and no longer have the disease... I dont like it honestly but know for incidence they want you to not include those with disease so i just went with dogma questions on incidence to get to 10% +  

submitted by drdoom(896),
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Also idosncer htis trage erocsnidipt fomr hte NI’Hs eMSH a:basdtea

CNEIICNDE: Teh uenmrb fo enw scsae of a nigev daissee igurdn a eivgn pdireo in a iecsdepif on.uopiptal It lsoa is usde rfo eth eart at which new nvstee ccrou ni a neifedd patl.opionu tI is deneftrditfeia form VERLCENPAE, ciwhh rrefes to lla cse,as wne ro dol, in hte iutaolppon at a negvi .tmei


questioneverything  The prevalence of chlamydia in this group would be 0. It is not a chronic disease. +  

submitted by usmle11a(77),
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eth iteqsonu dntoes ysa ttah eht 005 otg dcru,e so ti ilwl eb 2000 ohw rea at .skri