Standard deviation and variance -- What are they good for?

[Guest]

I have been thru a DOZEN Access "Bibles" looking for information about
variance and standard deviation. Never having taken stats in college, I am
CLUELESS as to what these numbers represent. And every publisher talks about
min, max, average, and sum, but won't explain or give examples of standard
deviation or variance. Could someone please help me understand? I'd
appreciate it. Access XP help isn't any more useful.

Jay

 

[Tom Lake]

I have been thru a DOZEN Access "Bibles" looking for information about

variance and standard deviation. Never having taken stats in college, I
am
CLUELESS as to what these numbers represent. And every publisher talks
about
min, max, average, and sum, but won't explain or give examples of standard
deviation or variance. Could someone please help me understand? I'd
appreciate it. Access XP help isn't any more useful.

There's a good explanation of SD here:

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

Tom Lake

 

[Guest]

Thank you, Tom. I had been there prior to writing.....I'm still having a
hard time grasping the concept. How could a group containing a series of
numbers (0, 6, 8, 14) have a standard deviation of 5???? I see the formula
being used to calculate, and I guess if it doesn't get easier than that, I'll
just have to live with it. This sort of thing never was my strong suit. I
had hoped there was a "Standard Deviation for Dummies" explanation some
place. Thanks anyway.

 

[Ed Robichaud]

In your example, the mean would be "7" and a calculated SD of "5". That
means that scores with a variance of +-5 (1 SD)from the mean (average)
constitute 66.6% of all scores and those +-10 (2 SD's) include 95% of all
scores.

-Ed

 

[Ed Warren]

Standard Deviation and Variance are measures of how much the values in the
data set vary from the average (mean)
a set of numbers like 5,4,4,5,6,4,5 would have a small variance
a set of numbers like 0,10,9,1,0,10,20 would have a large variance.
Standard Deviation is the square root of variance (so they are measuring the
same thing, just people have problems with getting their heads around
squared numbers)

Why are they important?

The daily average temperature in Omaha is the same as the daily average
temperature in San Francisco.
The variances (Standard Deviation) lets us know the climates are no-way the
same!!!

Why are they in Access? Lots of businesses use them for process control
(six-sigma, etc.)

Ed Warren.