+3SD (standard deviation)

[ferenc11]

Hi girls and boys!

Could any of yous explain to me what -3SD and +3SD mean? Why is it three?

I have the software CVCX (practicing every day) and am trying to get a clearer picture in my head what that widget means.
Replies greatly appreciated!
Thank you

Sent from my LG-H955 using Tapatalk

[ZenMaster_Flash]

Google: Standard Deviation.

[Meistro123]

A 3 std deviation occurrence is an extremely rare event, an outlier. Something that will happen about 4% of the time.

https://en.wikipedia.org/wiki/68%E2%...80%9399.7_rule

[Freightman]

A 3 std deviation occurrence is an extremely rare event, an outlier. Something that will happen about 4% of the time.

https://en.wikipedia.org/wiki/68%E2%...80%9399.7_rule

It can certainly happen, especially with enough rounds played. I've exceeded 3sd on both sides of the bell curve.

[RS]

Standard Deviation (SD or Std Dev) is how far away your actual results are from expected results -- ie: variance.

It's a way to express how likely or unlikely certain results are.

People use 3 SD's as a way to basically encompass everything that is possible. Of course, 4 SD's is also possible, and 5....but the probability of those is so low, you can for the most part, just throw those obscene chances out.

A 3 std deviation occurrence is an extremely rare event, an outlier. Something that will happen about 4% of the time.

https://en.wikipedia.org/wiki/68%E2%...80%9399.7_rule

I think you might have it mixed up. Being within 3 SD's is 99.73% chance. So being +3 SD or more up is half of 0.27%, or about 0.135% (about 1 in 740). Being down 3 SD's is the same, 0.135% or 1 in 740.


This is an interesting chart from the wikipedia link from Meistro:

Range	Expected Fraction of
Population Inside Range
Approximate Expected
Frequency Outside Range
Approximate Frequency for Daily Event
? ± 0.5?	0.382924922548026	2 in 3			Four times a week
? ± ?		0.682689492137086	1 in 3			Twice a week
? ± 1.5?	0.866385597462284	1 in 7			Weekly
? ± 2?		0.954499736103642	1 in 22			Every three weeks
? ± 2.5?	0.987580669348448	1 in 81			Quarterly
? ± 3?		0.997300203936740	1 in 370		Yearly
? ± 3.5?	0.999534741841929	1 in 2149		Every six years
? ± 4?		0.999936657516334	1 in 15787		Every 43 years (twice in a lifetime)
? ± 4.5?	0.999993204653751	1 in 147160		Every 403 years (once in the modern era)
? ± 5?		0.999999426696856	1 in 1744278		Every 4776 years (once in recorded history)
? ± 5.5?	0.999999962020875	1 in 26330254		Every 72090 years (thrice in history of modern humankind)
? ± 6?		0.999999998026825	1 in 506797346		Every 1.38 million years (twice in history of humankind)
? ± 6.5?	0.999999999919680	1 in 12450197393	Every 34 million years (twice since the extinction of dinosaurs)
? ± 7?		0.999999999997440	1 in 390682215445	Every 1.07 billion years (a quarter of Earth's history)

NOTE: Those probabilities are for being WITHIN +/- a given SD. For only being + or only being - a specific SD, cut the number or probability in half.