Statistics question

[Pulp, SASS#28319]

At the hospital we're staying at there are two elevators facing each other about 30feet apart. Each elevator has a call button, but each call button communicates with both elevators. I walk up to one or the other, push the call button, and one or the other elevators opens. I would think that the odds of one elevator opening would be 50/50. However After five days of using the elevators I am about 3 for 25 at standing by the elevator that opens. Am I just horribly unlucky, or is there more at work than here than simple 50/50?

 

I'm not much good at cipherin', bit could the odds actually be 1/4 since there are two buttons and two elevators? The choice of buttons is 50/50 since I have two to choose from, but since each button can call either elevator I can't figger out how that factors into the problem.

[Chickasaw Bill SASS #70001]

Pulp

 

Think about this , 2 buttons x 2 elevators x 2 places to wait = 1 in 8 to get it right

 

CB

[Crazy Gun Barney, SASS #2428]

From a statistics point of view, your odds are still 50/50. Think of it like the flip of a coin. Each flip has the same 50/50 odds. Even if the coin lands heads up 500 times in a row, the next flip still has a 50/50 chance. Trends are perceived, but are only imaginary, they have no real bearing on the situation. As the number of occurrences (flips of the coin, or elevator doors opening) approaches infinity, the true odds will be shown to be 50/50.

 

All that being said, do the 2 elevators go to all of the same floors? I have noticed sometimes that one elevator may access higher floors, or perhaps a basement when the other elevator doesn't. That will skew the odds. Or, in hospitals I have seen one elevator that is deep enough for a rolling bed to fit, while the other is for standing passengers only. This could mean one or the other is in use more often.

[Loophole LaRue, SASS #51438]

Funny the places a man's mind goes when he's hanging around a hospital waiting for a loved one to heal......

 

LL

[Pulp, SASS#28319]

Both elevators are equal in size and floors covered. Surgical and service elevators are elsewhere.

 

Bill, you may be right. 3/25 is real close to 1/8. The only thing I might question is the two buttons. Since each button can call either elevator, wouldn't it be the same if there was only one button?

[Chickasaw Bill SASS #70001]

Pulp

 

Think of it as a series/ parell circut , the switches will have to be wired that way , to feed the PLC .

 

therefore the S/P logic will apply ,

 

that being sometines , MAYBE , but NOT always

 

as with all electric curcits , you will also need to check the SMOKE pressure ,

 

Ya let the smoke out , it NO wor*ie

 

CB

[Curley Fryes]

Then there's the variable that one of the elevators may be out of service for one of the days.

[J. Mark Flint #31954 LIFE]

Pulp, the explanation is actually much simpler than all of this math. The elevator call buttons call for an elevator. The elevator controls are computerized and in their programing there has been some bias programed in in an attempt to keep the elevators working efficiently. ie, the elevators park themselves on specific floors so as to be able to provide faster service to those areas deemed to be more likely to need service. This can even be altered based upon time of day.

 

So to answer your original question . . . I prefer Mary Ann.

[Old Scatterbrain]

Is it possible that the system designates one of the elevators as primary? And I have been in more than one hotel where, in the rest state so-to-speak, one elevator is always "parked" at the first floor while the other one is parked at the top or midpoint.

 

EDIT Too slow once again :angry:

[Shooting Bull]

If I have a 50/50 chance of getting something right, I get it wrong 100% of the time.

 

Sour Kraut will vouch for this.

[Birdgun Quail, SASS #63663]

From a statistics point of view, your odds are still 50/50. Think of it like the flip of a coin. Each flip has the same 50/50 odds. Even if the coin lands heads up 500 times in a row, the next flip still has a 50/50 chance. Trends are perceived, but are only imaginary, they have no real bearing on the situation. As the number of occurrences (flips of the coin, or elevator doors opening) approaches infinity, the true odds will be shown to be 50/50.

 

 

 

Wow! That's almost a third of the time.

[Chickahominy Charlie]

Reminds me of my days in military school in Probability & Statistics class. As I remember, our questions were worded like this:

 

"Japanese Zeros, carrying bombs, are bombing battleships in Pearl Harbor. If each plane has 1 bomb and there are 6 planes making simultaneous bombing runs on the same battleship, what is the probability that the maiden-name of any one of the pilots' mothers on said attack is Nagasaki?"

 

Chick

[Noz]

Pulp, the explanation is actually much simpler than all of this math. The elevator call buttons call for an elevator. The elevator controls are computerized and in their programing there has been some bias programed in in an attempt to keep the elevators working efficiently. ie, the elevators park themselves on specific floors so as to be able to provide faster service to those areas deemed to be more likely to need service. This can even be altered based upon time of day.

 

So to answer your original question . . . I prefer Mary Ann.

Way to cut through all of the stuff and get to the real question.

 

I like Mary Ann too.

 

 

 

 

 

One of my many stays in the hospital with my father(17 years on dialysis) I counted the holes in an acoustical tile on the ceiling in his room. Then multiplied by the number of tiles in his room then the number of rooms on the floor, then the number of tiles in the hall and then decided if I expanded any more the fellows in the white coats would come and get me. The nurses were looking strangely at the big guy walking the halls and mumbling to himself.

[Marshal Mo Hare, SASS #45984]

Did you make a note of which elevator showed up? Or just that you were only right 3 times?

[J-BAR #18287]

As others have pointed out, you are dealing with more than one variable. You can't determine your odds for a successful prediction until you know the actual behavior of the elevators. Your chances would be 50-50 only if the elevators visited your floor at the exact same frequency over a long period of time AND their arrivals were truly random. Under those conditions you could always choose the same elevator and be sure you had a 50/50 chance. As others have pointed out, there is likely to be bias in their programming.

 

You could use statistics to determine their programming; tracking which one opens versus time of day over several day's time. Basing your choice on that knowledge, you could predict which one opens first with a high degree of accuracy...you could do a lot better than 50/50.

[Krazy Kajun]

Pulp, the explanation is actually much simpler than all of this math. The elevator call buttons call for an elevator. The elevator controls are computerized and in their programing there has been some bias programed in in an attempt to keep the elevators working efficiently. ie, the elevators park themselves on specific floors so as to be able to provide faster service to those areas deemed to be more likely to need service. This can even be altered based upon time of day.

 

If it were a true random selection then 50/50 would be the answer. What J. Mark said is exactly what is used in elevators systems in larger buildings.

 

1. Taller buildings may have certain elevators that go to the higher floors and banks that work only in the lower floors. This is used to provide better service to each of the two parts of the building...lower wait times and such.

 

2. Larger hotels do have elevators that park on certain floors during differing times of day to provide faster response time...such as during the peak check in and check out times.

 

3. Then there is another bias called duty cycling whereby for elevators that are utilized in a defined part of a building are used on a programmed alternating basis to provide the same amount of work or duty for each of the elevators in the bank....prevents one elevator from being used more than others.

 

4. Then there is just plain old random dumb luck where some elevators are out of service and it all goes to hell in a hand basket....true randomness.

 

At any rate...the intent is lower wait times but sometimes I think the same folks that program elevators also program traffic lights....but that's a whole 'nother thread. I went to a traffic control course in Hot Springs Arkansas several years back and that stuff gets to be mind boggling. Glad I'm past that part in my career where I had to program traffic signals...that kind of stuff is for younger minds.

[Badger Mountain Charlie SASS #43172]

No matter what the statistics are, the elevator will be full when it gets to my floor.

[Pulp, SASS#28319]

Traffic lights are another thing I have bad luck with. I believe Oklahoma City has an ordinance that states: All traffic signals must turn red as Pulp approaches.