# Confidence & Reliability - Reference to a 90/95 Confidence & Reliability Level

T

#### teqp1

Re: Confidence and Reliability - Reference to a 90/95 confidence and reliability leve

Juan Dude,

Thanks again, that was the book I was able to locate as well. Appreciate the help!

I have used that online calculator as well as a quick check in the past.

Agreed, it would be nice to see in an Excel sheet.

Thanks again.

#### Tim Folkerts

Trusted Information Resource
Re: Confidence and Reliability - Reference to a 90/95 confidence and reliability leve

Hot off the presses ... here's the Excel Spreadsheet! I added a couple extra lines for more options. But you can type in any values for confidence an reliability and get the required size in the table.

Tim F

#### Attachments

• Reliability & Confidence.xls
18.5 KB · Views: 1,383
J

#### Juan Dude

Re: Confidence and Reliability - Reference to a 90/95 confidence and reliability leve

Hot off the presses ... here's the Excel Spreadsheet! I added a couple extra lines for more options. But you can type in any values for confidence an reliability and get the required size in the table.

Tim F
Thank you Tim

I don't know if it's possible but a C/R calculator for Variable data would be awesome.

T

#### teqp1

Re: Confidence and Reliability - Reference to a 90/95 confidence and reliability leve

Thank you all for your help. I appreciate all the quick replies.

T

#### teqp1

Re: Confidence and Reliability - Reference to a 90/95 confidence and reliability leve

I think I finally have enough posts to add a link to the original table I was referring to in my previous post. As you can see, pretty much the same as Juan Dude's version.

Last edited by a moderator:
R

#### rebecca.hess

Re: Confidence and Reliability - Reference to a 90/95 confidence and reliability leve

[SIZE=-1][FONT=arial,helvetica,sans-serif]Given R=.95, C = .90 , solve for n[/FONT][/SIZE]
[SIZE=-1][FONT=arial,helvetica,sans-serif]Ln(R)=(1/n)*Ln(1-C)[/FONT][/SIZE]
[SIZE=-1][FONT=arial,helvetica,sans-serif]-.05129=(1/n)*(-2.30259)[/FONT][/SIZE]
[SIZE=-1][FONT=arial,helvetica,sans-serif]n= 44.89 or 45.[/FONT][/SIZE]

I am confused...
How does (1-C), or (1-.90), turn into (-2.30259)????
A little math lesson please... anyone...

#### Miner

##### Forum Moderator
Re: Confidence and Reliability - Reference to a 90/95 confidence and reliability leve

I am confused...
How does (1-C), or (1-.90), turn into (-2.30259)????
A little math lesson please... anyone...
You overlooked Ln(1-C). That is the Natural logarithm of (1-C).

Ln(.1) = -2.30259

R

#### rebecca.hess

Re: Confidence and Reliability - Reference to a 90/95 confidence and reliability leve

Logs... Duh, thanks!!

#### Jim Wynne

Re: Confidence and Reliability - Reference to a 90/95 confidence and reliability leve

Logs... Duh, thanks!!

Logger rhythm:

R

#### rebecca.hess

Re: Confidence and Reliability - Reference to a 90/95 confidence and reliability leve

Working on a process PQ with a customer and having trouble with some of the sample size logic. Any help would be appreciated!

Customer is requesting a 95/95 confidence/reliability level which calculates to 59 pcs. If we are running 3 lots of product in order to evaluate run-to-run variation under normal operating conditions, do we need 59 pcs from each run? Customer is requesting 20 pcs from each run be combined into one study. This sounds a little strange to me.

In addition, we are looking to qualify the process using 2 sets of equipment to allow for flexibility in the manufacturing process. The process has 3 steps, each step with a primary and an alternate machine. Sooo... 3 runs of 60 pcs on each possible combo of equipment??