
Probability and Statistics Basic Probability and Statistics Math Forum 
 LinkBack  Thread Tools  Display Modes 
March 25th, 2016, 12:41 PM  #1 
Newbie Joined: Mar 2016 From: Earth Posts: 4 Thanks: 0  Multiple Occurrences of Negative Events
Suppose we have a ball which has a chance of being dropped and a chance of remaining where it is. Let the chance of the ball dropping be y and let the chance of the ball remaining where it is be a. Thus the chance of the ball dropping four times is y x y x y x y. One might suggest doing the same with a, but something seems off. How could the ball 'not drop' multiple times, this is not the same as 'not getting heads' which constitutes a different event 'getting tails' because in this cause 'not dropping' is the same as saying 'no relevant event is happening'. This is obviously a negative event, in the sense that it is an event constituted by something not happening. How many times does this event occur, every second? How can we treat it as an event when it is by definition the lack of an event, doesn't this seem rather like treating nothing as something? Are negative events just mathematical devices? If so, why do we treat them like genuine events? 
March 25th, 2016, 03:55 PM  #2 
Global Moderator Joined: May 2007 Posts: 6,788 Thanks: 708 
The whole scenario makes sense if there are discrete attempts to drop the ball.

March 25th, 2016, 05:49 PM  #3 
Newbie Joined: Mar 2016 From: Earth Posts: 4 Thanks: 0 
But there could just as easily not be.

March 26th, 2016, 09:58 AM  #4 
Newbie Joined: Mar 2016 From: United Kingdom Posts: 2 Thanks: 1 
When assigning a probability to an event you need to define limits for your "trial". For example "Suppose we have a ball which has a probability y of being dropped in the next hour (day, week, year whatever). Or "Suppose we have a ball which has a probability a of remaining where it is before teacher returns to the classroom (next fall of snow)". For each case, either the ball remains to the end of the "trial" or it drops when you perhaps replace it for a new "trial".

March 26th, 2016, 10:48 AM  #5  
Senior Member Joined: Jun 2015 From: England Posts: 915 Thanks: 271  Quote:
Note the other respondents used the word probability which is tightly defined. Chance and probability do not mean the same.  

Tags 
event, events, multiple, negative, occurances, occurrences 
Thread Tools  
Display Modes  

Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Calculate the probability of 0 or 2+ occurrences  Parlo  Probability and Statistics  1  July 30th, 2014 06:12 PM 
Manipulation of negative square root of a negative term/#  daigo  Algebra  3  June 30th, 2012 07:06 AM 
probability of multiple events with multiple trials  prwells32  Advanced Statistics  4  January 30th, 2010 02:42 PM 
Calculating Probabilities of Occurrences  CBSte  Algebra  1  July 8th, 2009 01:48 PM 
Are these events, even possible?  MyNameIsVu  Applied Math  2  April 23rd, 2009 04:07 PM 