
Probability and Statistics Basic Probability and Statistics Math Forum 
 LinkBack  Thread Tools  Display Modes 
September 2nd, 2017, 01:43 PM  #1 
Newbie Joined: Sep 2017 From: Oxford Posts: 1 Thanks: 0  Probability re Placebo
Any help appreciated to calculate the below. A clinical trial has two arms. Arm 1 is placebo. The results generated were 17 responders out of 44 patients (38.6%) Arm 2 is the active trial. The results generated were 49 responders out of 90 patients (54.4%) How do I calculate the p number to show the likelihood of the active arm obtaining that statistical result by chance, i.e. the chance of there being no real difference between the active arm and placebo? Anything under p=0.05 will be statistically significant, which is what I am trying to assess. Thanks in advance Last edited by siciliankan; September 2nd, 2017 at 01:44 PM. Reason: Extra information 
September 10th, 2017, 05:17 AM  #2 
Member Joined: May 2013 Posts: 33 Thanks: 1 
so lets create the probability square. Code: prob(react to placebo)  prob(not react to placebo)  prob(react to actual)  49/90  prob(not react to actual)  41/90  17/44  27/44  1 
October 27th, 2017, 12:25 PM  #3 
Newbie Joined: Oct 2017 From: US Posts: 11 Thanks: 0 
Just put the following numbers into this chisquare calculator 17 27 49 41 you will get a p value of 0.085631065798, which is larger than 0.05. Therefore, it is not significant at 0.05 level and you can not reject the null hypothesis of independence that placebo and trial are the same in 'react or not'. Last edited by James White; October 27th, 2017 at 12:43 PM. 

Tags 
placebo, probability 
Thread Tools  
Display Modes  

Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Continuous probability; find probability density function  rivaaa  Advanced Statistics  5  November 5th, 2015 02:51 PM 
probability set theory  probability of x out of n events  hbonstrom  Applied Math  0  November 17th, 2012 08:11 PM 
Joint probability density function, probability  token22  Advanced Statistics  2  April 26th, 2012 04:28 PM 
Probability (probability mass function,pmf)  naspek  Calculus  1  December 15th, 2009 02:18 PM 