Go Back   AnandTech Forums > Hardware and Technology > Memory and Storage

Forums
· Hardware and Technology
· CPUs and Overclocking
· Motherboards
· Video Cards and Graphics
· Memory and Storage
· Power Supplies
· Cases & Cooling
· SFF, Notebooks, Pre-Built/Barebones PCs
· Networking
· Peripherals
· General Hardware
· Highly Technical
· Computer Help
· Home Theater PCs
· Consumer Electronics
· Digital and Video Cameras
· Mobile Devices & Gadgets
· Audio/Video & Home Theater
· Software
· Software for Windows
· All Things Apple
· *nix Software
· Operating Systems
· Programming
· PC Gaming
· Console Gaming
· Distributed Computing
· Security
· Social
· Off Topic
· Politics and News
· Discussion Club
· Love and Relationships
· The Garage
· Health and Fitness
· Merchandise and Shopping
· For Sale/Trade
· Hot Deals with Free Stuff/Contests
· Black Friday 2014
· Forum Issues
· Technical Forum Issues
· Personal Forum Issues
· Suggestion Box
· Moderator Resources
· Moderator Discussions
   

Reply
 
Thread Tools
Old 07-01-2012, 03:57 PM   #76
Obsoleet
Platinum Member
 
Obsoleet's Avatar
 
Join Date: Oct 2007
Location: Austin, Texas
Posts: 2,184
Default

Quote:
Originally Posted by Schmide View Post
Actually by statistics, to have a confidence level of 95+-10% for 7million people, you need a sample size of 96.

It goes up sharply if you need 95+-5%, for that you'd need a sample size of 384.

All this does not include high bias trends. If the trending statistics are in the 10% level, you only need 139 to reach a 95+-5% confidence level. At 5% 73.
Owned
Obsoleet is offline   Reply With Quote
Old 07-01-2012, 04:02 PM   #77
Railgun
Senior Member
 
Railgun's Avatar
 
Join Date: Mar 2010
Location: ORD-->LHR
Posts: 965
Default

Quote:
Originally Posted by Obsoleet View Post
Owned
No need for the peanut gallery to chime in, especially with hugely useless posts.

I'm a network engineer, not a mathematician. That said, let's see from where/who they got this sample, how large it was and from what the overall group size is.
Railgun is offline   Reply With Quote
Old 07-01-2012, 04:21 PM   #78
Obsoleet
Platinum Member
 
Obsoleet's Avatar
 
Join Date: Oct 2007
Location: Austin, Texas
Posts: 2,184
Default

Quote:
Originally Posted by Railgun View Post
No need for the peanut gallery to chime in, especially with hugely useless posts.

I'm a network engineer, not a mathematician. That said, let's see from where/who they got this sample, how large it was and from what the overall group size is.
Statistics != Math.
http://www.stat.purdue.edu/~dsmoore/...s/Statmath.pdf
http://simplystatistics.org/post/209...cs-is-not-math
Obsoleet is offline   Reply With Quote
Old 07-01-2012, 04:54 PM   #79
jwilliams4200
Senior Member
 
Join Date: Apr 2009
Posts: 532
Default

I looked around for a suitably simple tutorial on sample estimation and confidence intervals so that those who are not familiar with the subject could understand it. I found a pretty good tutorial aimed at high school AP students:

http://stattrek.com/estimation/confi...px?tutorial=ap

Hopefully a "network engineer" should have enough math and logic background to follow it.

Now to take a specific example, let's look at the return rates for a given manufacturer, and say the sample size is 500 (the minimum allowed for inclusion in the BeHardware study). Also assume that the total population of parts produced by the manufacturer is much more than 500 (at least 10 times more) and that the sample had 10 returns for a return rate of 10/500 = 2%

Then just follow the recipe given in the link above. We assume it is a random sample (there is no reason to believe that the manufacturer cherry-picked parts to send to this etailer), there were at least 10 (or 5) failures. The population size is much larger than 500, so we can use the approximate formula for the standard error:

SE = sqrt( p * q / n ) = sqrt( 0.02 * 0.98 / 500 ) = 0.00626

It is convenient to go for a 95% confidence interval (since margin of error is equal to about 2 SEs, or more precisely 1.96 SE)

Then ME = 1.96 * 0.00626 = 0.0123

So the 95% confidence interval is 0.02 +/- 0.0123

Not an especially narrow interval, but that is why the BeHardware study chose 500 as the minimum sample size. Larger samples will have narrower intervals. Also, larger return rates will have intervals with widths proportionally smaller compared to the return rate.

Last edited by jwilliams4200; 07-01-2012 at 05:03 PM.
jwilliams4200 is offline   Reply With Quote
Old 07-01-2012, 04:56 PM   #80
Schmide
Diamond Member
 
Schmide's Avatar
 
Join Date: Mar 2002
Posts: 4,235
Default

Quote:
Originally Posted by Railgun View Post
That said, let's see from where/who they got this sample, how large it was and from what the overall group size is.
What the math is saying though. It matters not where they got the sample or how large the overall group is; because, if the variation and trend are small, the confidence will be high.

When trend is such low number 0-15%, the sample size needs to be relatively small as well.

Summing up.

100+ samples
1 product
<15% trend
equals
95+-5% confidence

edit:

Quote:
Originally Posted by Obsoleet View Post
Statistics != Math.
What?
__________________
All errors are undocumented features waiting to be discovered.

Last edited by Schmide; 07-01-2012 at 05:00 PM.
Schmide is online now   Reply With Quote
Old 07-01-2012, 05:58 PM   #81
Obsoleet
Platinum Member
 
Obsoleet's Avatar
 
Join Date: Oct 2007
Location: Austin, Texas
Posts: 2,184
Default

Quote:
Originally Posted by Schmide View Post
What?
Links provided above
Obsoleet is offline   Reply With Quote
Old 07-01-2012, 06:06 PM   #82
jwilliams4200
Senior Member
 
Join Date: Apr 2009
Posts: 532
Default

Quote:
Originally Posted by Obsoleet View Post
Links provided above
Can we NOT get into a semantic argument over whether statistics is mathematics or applied mathematics?
jwilliams4200 is offline   Reply With Quote
Old 07-02-2012, 11:31 PM   #83
borisvodofsky
Diamond Member
 
Join Date: Feb 2010
Posts: 3,606
Default

Very true, I know this chick who's a statistician, she's HORRIBLE at math. And she wanted to be an actuary, HAHAHAHAHAHA, maybe if she grinded 9-10 combinatorics books.
__________________
2500k | 4.8ghz | 1.33v
borisvodofsky is offline   Reply With Quote
Old 07-02-2012, 11:31 PM   #84
borisvodofsky
Diamond Member
 
Join Date: Feb 2010
Posts: 3,606
Default

Quote:
Originally Posted by jwilliams4200 View Post
Can we NOT get into a semantic argument over whether statistics is mathematics or applied mathematics?
This isn't a semantic argument, statistics is very very very very different from real math.
__________________
2500k | 4.8ghz | 1.33v
borisvodofsky is offline   Reply With Quote
Old 07-02-2012, 11:34 PM   #85
borisvodofsky
Diamond Member
 
Join Date: Feb 2010
Posts: 3,606
Default

Quote:
Originally Posted by Railgun View Post
No need for the peanut gallery to chime in, especially with hugely useless posts.

I'm a network engineer, not a mathematician. That said, let's see from where/who they got this sample, how large it was and from what the overall group size is.
railgun, give up bro, the stat guy won this one. .
__________________
2500k | 4.8ghz | 1.33v
borisvodofsky is offline   Reply With Quote
Old 07-02-2012, 11:39 PM   #86
jwilliams4200
Senior Member
 
Join Date: Apr 2009
Posts: 532
Default

Quote:
Originally Posted by borisvodofsky View Post
This isn't a semantic argument
Can we NOT get into an argument about the meaning of "semantic"?
jwilliams4200 is offline   Reply With Quote
Old 07-03-2012, 12:03 AM   #87
borisvodofsky
Diamond Member
 
Join Date: Feb 2010
Posts: 3,606
Default

Quote:
Originally Posted by jwilliams4200 View Post
Can we NOT get into an argument about the meaning of "semantic"?
you mad bro?
__________________
2500k | 4.8ghz | 1.33v
borisvodofsky is offline   Reply With Quote
Old 07-03-2012, 08:02 AM   #88
jwilliams4200
Senior Member
 
Join Date: Apr 2009
Posts: 532
Default

No
jwilliams4200 is offline   Reply With Quote
Reply

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 12:49 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.