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NBME 21 Answers

nbme21/Block 4/Question#11 (32.7 difficulty score)
A study is conducted on patients with asthma ...
If the treatment really changes the mean asthma score by 0.4, there is an 80% chance that a study of this size will find a p-value < 0.05🔍

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 +6  upvote downvote
submitted by imgdoc(127),
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csylliBaa hist qionuste tusj assk thwa" si weo"rp dna ssak oyu ot aenlpix htta %08 wpro.e owrPe si 1 - tbae e(typ 2 )rro,er baclalsyi enwh a fenfeeidcr seitsx adn teh lnul hsopsithey si edtjecre si woep.r So fi teh xR cedtset a naem fecerdfien of 4.0 in mathas in teh atitsepn ni hte ntrtaeemt rgu,po nhte taht adta lfals in eht 08% porwe e,ganr nda sit nncfiagsecii is %95 0;5.()lpt&,0 P avuel is utjs hte pbioriaylbt of mteonihgs ngapepnih by aenh,cc so you ahwt itsh to be less hatt 5% os tevhrwea oyu bvsedore st'in ihbls.lut

I hoep shit ehpe,dl dan ocertcr em fi I'm .gwnro

yssya1992  I have a question : whats the relation then between power and P value ? +  
privatejoker  This one took me a minute and was during the last block so my brain was already fried. But my reasoning was that, as stated above, since it gave you power, it is basically just a long-winded way of asking what Power is, and how this relates to p-value. P-value is the odds that the finding was due to chance alone. Obviously a p-value set to <0.05 implies a greater than 95% chance that the finding is legit. Since the power is said to be 80%, this means that there is an 80% chance that the study finding is legit, at least insomuch that it met the pre-set criteria of being 95% non-chance related. +  
sahusema  80% chance (power) the study correctly identifies the existence of an association in reality. If an association is determined to exist, >95% chance the study and reality agree with each other (p<.05) +1  

 +3  upvote downvote
submitted by nosancuck(73),
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Bklac hPowa!

oaPwh = 1 - AETB = ad trae fo med ERTU ETPSIS;IOV uwz da erta ta ihwhc oyu get da etru teovissip sorcsa a nhcuab ts?sediu 80% here hbur

lostweightthxnorovirus  wherever you learned biostats I wanna learn ;) +9  
djinn  Sensitivity is the rate of true positives. Beta is the rate of false negatives. +  
helsinki  ... yeah you're definitely a white man +  

 +1  upvote downvote
submitted by andro(109),


First Step : Power is probability or chance ( that a study will detect a true difference) . So cancel out every single option that says 80 % of subjects ( And I mean every single one of them !!) which is basically every single option from A to D

Second Step : this leaves you with only option E and F which are now questioning your understanding of the p value ( again a probability /chance thats a study will detect a difference when none exists ) In our study all the values obtained were associated with a p value of 0.035 i.e less than 0.05.

Third Step : Pick option F

You will find that most of these questions are just a play on words - 80 % probability vs 80 % of subjects to test whether you understand what the term really means

 +1  upvote downvote
submitted by sahusema(117),
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08% chenca ewr(po) eth tsudy ccoeyrrtl tfeiseindi eth xctneiese of na cnosstoiiaa in atlyeri. If an sicatnsaioo is edrnedimet ot sx,eti &5gt9%; ccahne eht yustd dna rlayite raege twih hcae heort (t5l.)p0&;

 +0  upvote downvote
submitted by brasel(7),

Power = ability to detect a difference between groups (if one exists) P value (<0.05) = probability that results were due to random chance

80% power = 80% chance of the study being able to detect symptom changes, which in this case was 0.4 (AKA 80% chance of detecting a significant p value)