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Tags probability , uncertainty

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Old 18th August 2008, 01:59 AM   #1
Ivor the Engineer
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How do you handle probabilistic knowledge?

No events in life have a probability of 0 or 1 of occurring. Statistical information is rarely available about us as individuals, so we have to rely on averages of groups and assume we share many of the significant characteristics of a particular group if we wish to use the data in our decisions.

What behaviours (if any) do you engage in where you expect to beat the odds?

Is this an irrational way to behave?
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Old 18th August 2008, 03:04 AM   #2
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Due to my crippling fear of any kind of injury, I used to stay in bed with the covers over my head. Then I heard that most accidents happen within one mile of your home, so I wander the streets 24x7, sleeping in doorways. That way, I'll never be hurt and will probably live forever.
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Old 18th August 2008, 03:04 AM   #3
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Originally Posted by Ivor the Engineer View Post
What behaviours (if any) do you engage in where you expect to beat the odds?
I have a crappy diet. Not enough fruits and vegatables. Too much meat.

Quote:
Is this an irrational way to behave?
Yes.
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Old 18th August 2008, 03:29 AM   #4
Ivor the Engineer
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Here's some info. on speed and accidents.

http://www.erso.eu/knowledge/content...oad_safety.htm

One particularly interesting bit:

Quote:
Speeding: societal vs. individual consequences

The negative road safety outcomes of high speed are evident at an aggregate level. At the level of the individual driver, the risk of an accident is very small; at higher speeds the risk is higher, but still very small. Hence, an individual driver will hardly ever experience the safety consequences of excess speed. More or less the same applies for the environmental effects of speeding. These are also noticeable at an aggregate level, but hardly at the individual level (possibly with the exception of fuel consumption).

Contrary to the disadvantages, the advantages of higher speeds are experienced at the individual level. Individual advantages include just reaching traffic lights while still green, (subjectively) shorter journey times, thrill and enjoyment of speed or speeding.

This contradiction between societal and individual consequences makes persuading drivers of the value of speed management a difficult mission.
ETA: What has slowed me down is having a display of mpg on the dash. Whereas I would regularly travel at 80-90mph on motorways in my previous car with no such display, I now average 60-75mph.

Last edited by Ivor the Engineer; 18th August 2008 at 03:36 AM.
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Old 18th August 2008, 03:47 AM   #5
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Can people with more driving experience and/or higher performance (i.e. better braking) vehicles drive faster than average without increasing their risk above the group?
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Old 18th August 2008, 03:52 AM   #6
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Maybe some can, but it shouldn't be down to an individual to decide whether they are in that group. Many people think they are more skilled than they are.

http://www.apa.org/journals/features/psp7761121.pdf
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Old 18th August 2008, 04:21 AM   #7
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Originally Posted by Ivor the Engineer View Post
Here's some info. on speed and accidents.

One particularly interesting bit:



ETA: What has slowed me down is having a display of mpg on the dash. Whereas I would regularly travel at 80-90mph on motorways in my previous car with no such display, I now average 60-75mph.
Wow, 80-90 is pretty excessive on most highways around me. I suppose the MPG display brings the relationship a bit closer to the wallet and few things change habits like that.
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Old 18th August 2008, 04:28 AM   #8
Jeff Corey
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That is similar to the Lake Wobegon Effect. http://changingminds.org/explanation...e_woebegon.htm
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Old 18th August 2008, 04:46 AM   #9
JoeEllison
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Originally Posted by Professor Yaffle View Post
Maybe some can, but it shouldn't be down to an individual to decide whether they are in that group. Many people think they are more skilled than they are.
As far as driving is concerned, I'm pretty sure I'm pretty good at it. I drive the speed limit and avoid tailgating because I don't trust the rest of you wackos!
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Old 18th August 2008, 04:55 AM   #10
Ivor the Engineer
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Originally Posted by jdp View Post
Wow, 80-90 is pretty excessive on most highways around me. I suppose the MPG display brings the relationship a bit closer to the wallet and few things change habits like that.
Yeah, it appeals to both my natural tightness and provides an alternative (and no doubt less risky) game to minimising journey time. I now regularly average 60mpg. I've yet to figure out if I save more fuel by free-wheeling down hills or using the engine to brake the acceleration.
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Old 18th August 2008, 05:08 AM   #11
Ivor the Engineer
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Originally Posted by Professor Yaffle View Post
Maybe some can, but it shouldn't be down to an individual to decide whether they are in that group. Many people think they are more skilled than they are.

http://www.apa.org/journals/features/psp7761121.pdf
Can having knowledge of our tendency to over-estimate our performance in comparison to others guard against doing it?

Last edited by Ivor the Engineer; 18th August 2008 at 05:22 AM.
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Old 18th August 2008, 05:35 AM   #12
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Odds are, we will all die some day. So, I recommend against life of any sort, as it always seems to end badly.
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Old 18th August 2008, 06:42 AM   #13
Ivor the Engineer
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An interesting article in wiki on risk perception:

http://en.wikipedia.org/wiki/Risk_perception

Quote:
A key early paper was written in 1969 by Chauncey Starr.[1] Starr used a revealed preference approach to find out what risks are considered acceptable by society. He assumed that society had reached equilibrium in its judgment of risks, so whatever risk levels actually existed in society were acceptable. His major finding was that people will accept risks 1,000 greater if they are voluntary (e.g. driving a car) than if they are involuntary (e.g. a nuclear disaster).
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Old 18th August 2008, 09:17 AM   #14
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Originally Posted by Ivor the Engineer View Post
Can having knowledge of our tendency to over-estimate our performance in comparison to others guard against doing it?
For some people, yes; for others, no.

I'm specifically thinking about Puthoff and Targ, who would write down all the ways they could think of that their paranormal experiment could be confounded by a cheating subject... and then do nothing to mitigate it.

They felt that by merely being 'aware of' the problem, they had eliminated it as a factor.
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Old 18th August 2008, 09:39 AM   #15
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Originally Posted by Mashuna View Post
Due to my crippling fear of any kind of injury, I used to stay in bed with the covers over my head. Then I heard that most accidents happen within one mile of your home, so I wander the streets 24x7, sleeping in doorways.
A few years ago I also heard that most accidents happen within one mile of your home, so I moved to a different house that was 3 miles away.
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Old 18th August 2008, 09:45 AM   #16
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Originally Posted by Ivor the Engineer View Post
No events in life have a probability of 0 or 1 of occurring. Statistical information is rarely available about us as individuals, so we have to rely on averages of groups and assume we share many of the significant characteristics of a particular group if we wish to use the data in our decisions.

What behaviours (if any) do you engage in where you expect to beat the odds?

Is this an irrational way to behave?
Poker, Craps, and Blackjack

I love gambling. Unfortunately only in Poker do I beat the odds and win. Well I don't really beat the odds. I get the same amount of flushes and full houses as everyone else, i just lose less when i lose and win more when i win.
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Old 18th August 2008, 10:15 AM   #17
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Originally Posted by JoeEllison View Post
As far as driving is concerned, I'm pretty sure I'm pretty good at it. I drive the speed limit and avoid tailgating because I don't trust the rest of you wackos!
It's much safer to try to match the speed of traffic than to drive the speed limit (assuming there is traffic). I would like to do that, but the usual traffic speed here is 15-20 mph over the limit, and I'm not comfortable knowing I could get a speeding ticket at any time, so I usually drive 5-10 over. I'm sure that increases the chance of my having an accident quite a bit, since cars are constantly tailgating and swerving around me. Driving at the speed limit would be much more dangerous, since there would be many more cars tailgating and swerving around, and many of those drivers would be steaming.
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Old 18th August 2008, 10:19 AM   #18
sol invictus
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Originally Posted by Bob Klase View Post
A few years ago I also heard that most accidents happen within one mile of your home, so I moved to a different house that was 3 miles away.
There's a sign on a road I sometimes take that says "dangerous curves". I always accelerate so as to spend as little time in the dangerous area as possible!
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Old 18th August 2008, 10:22 AM   #19
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Originally Posted by Ivor the Engineer View Post
...Statistical information is rarely available about us as individuals, so we have to rely on averages of groups and assume we share many of the significant characteristics of a particular group if we wish to use the data in our decisions.
According to what I've read, extrapolating from the group (nomothetic) to the individual (idiographic) is one of the most frequently committed logical fallacies, although the sources I've read may not be the final word on this argument. I guess we have to use something as a guide. Regarding relying on statistics of central tendency, I always think about Stephen J. Gould's essay The Median Isn't the Message; these numbers alone can be way off for us individually, and averages can be heavily influenced by outliers (e.g., in skewed distributions).

Another factor to consider alongside the actual mean or median or mode is the variability about those values in the distribution as a whole. Puts a nice backdrop to the statistical picture that we can consider.

Lastly, carefully crafted and conducted single-n (case) studies can actually be more helpful than many people think when lots of them are done and when the proper methodology is employed (repeated measures, time-series designs; see Single Case Experimental Designs by Barlow, Nock, & Hersen). Although it will never be spot-on, if an individual constellation of variables very closely approximates your own, there may be some value to using it as a predictive tool in limited cases. This is especially true in psychotherapy research, where certain single-n study clusters have been shown to be excellent in gauging treatment efficacy and underlying mechanisms of action. Information does and can get lost when you lump heterogeneous groups of people together.
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Old 18th August 2008, 10:25 AM   #20
Mashuna
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Originally Posted by sol invictus View Post
There's a sign on a road I sometimes take that says "dangerous curves". I always accelerate so as to spend as little time in the dangerous area as possible!
Which reminds me, I've got a Monica Bellucci film to watch tonight.
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Old 18th August 2008, 01:21 PM   #21
Ivor the Engineer
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http://en.wikipedia.org/wiki/Cultural_Theory_of_risk

So which best describes you: Individualist, Egalitarian, Hierarchist, Fatalist or Autonomous?

Personally, I think I'm pretty evenly spread between Egalitarian Individualist and Hierarchist. I blame my parents.

Last edited by Ivor the Engineer; 18th August 2008 at 01:48 PM. Reason: Egalitarian!? What was I thinking when I typed that?
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Old 19th August 2008, 02:00 AM   #22
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Here's a couple of pages which describe how we struggle to comprehend probabilistic information and gives some examples of ways of presenting it which may make such information easier or more difficult to grasp.

http://www.medicine.ox.ac.uk/bandoli...28/b128-6.html

Quote:
Study

The setting was 120 adult patients attending a cardiac rehabilitation clinic after bypass surgery or myocardial infarction, and taking simvastatin or atorvastatin. The only exclusions were inability to read or where first language was not English.

There were two variables. Two different adverse events of statins were chosen, constipation and pancreatitis, and the adverse event information was presented using words or numbers (Presentation Box below), using EU guidelines (Table 1). Half of the participants received information about constipation, and the other half information about pancreatitis (atorvastatin users only). Within each group, half received the information using words, and half using numbers. Allocation was random.


Results

The age range of participants was 35 to 74 years (median 63), and they had been taking a statin for one to 70 months (median six). The majority (56%) had no formal educational qualifications.

For both constipation and pancreatitis, participants overestimated the percentage chance of the adverse event affecting them (Figure 1). The degree of overestimation was far higher using words than using numbers. Using words rather than numbers also increased patient estimates of the event happening to them using a six point scale, with small differences in some other questions, and satisfaction with information presented was somewhat higher with numbers than with words.
http://www.medicine.ox.ac.uk/bandoli...44/b144-3.html

Quote:
Risk perception and presentation

A study [1] was carried out on two groups, 38 graduate students and 47 healthcare professionals. A hypothetical situation about adverse events of an influenza vaccine was presented to them in either a probability format (5%), or a frequency format (1 in 20). Randomisation was by alternation in questionnaire handouts.

The questionnaire asked whether they would be prepared to receive a vaccine if the risk of fever and headache within seven days was either 5% (one group) or 1 in 20 (the other). A second question asked participants to match frequency with one of six phrases, from very common to very rare.


Results

There was no difference between occupation, age, or sex of the groups receiving information as probability or frequency. About 60% of participants would have elected to have the influenza vaccine, without any significant difference between a probability format (67% electing to receive it) and the frequency format (55%).

There were differences between the way in which the risk was matched to phrases (Figure 1). In both presentations, the same risk was labelled as very common, through to rare. Presentation as frequency (1 in 20) resulted in much greater consensus, with 84% happy that this could be called common or occasional, and only 9% considering it either rare or very common.
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