Tim Folkerts
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Tim Folkerts replied to the topic probability question in the forum General 17 years, 11 months ago
a) First find the probabilty of drawing ggy in that order.
The odds that the first is g is 5/15
The odds that the second is g is 4/14
The odds that the third is y is 7/13The total odds are (5/15)*(4/14)*(7/13) = 0.05128Now, you can draw them in three different orders (ggy, gyg, or ygg) so the odds of any of these three are
0.0528*3 =…[Read more] 
Tim Folkerts replied to the topic Central Composite Design in the forum General 18 years ago
I’d like to refine a bit of what Bob J said.
1) A 2level factorial design is embedded in a CCD, but it can have any number of factors. Most typically people use 3 or 4 factors. (2 factors is almost too simple for RSM, while 5+ factors requires more experiments than most people are usually willing to run.)
2) CCD can be 3 levels, but typi…[Read more] 
Tim Folkerts replied to the topic Need interpretation in the forum General 18 years ago

Tim Folkerts replied to the topic Averaging averages – ???? in the forum General 18 years ago
If I read the question correctly then the simple answer is “no!”
To find an overall average, you NEED to do a weighted average, where each value is weighted by the FTE at that site. If you don’t know the FTE, you can’t find the answer.
For an extreme example:
Site 1: 2 employees; 1 is sick all week. They report average time lost is 20 hr/we…[Read more] 
Tim Folkerts replied to the topic Calculation of defect level in the forum General 18 years ago
First of all, we need to assume some distribution, and the binomial would be appropriate for this circumstance (assuming the defects are indeed randomly distributed). Using Excel, it is easy to generate a table of values with the odds of getting any number of defects. Below I’ve pasted the results: column 1 = # of defects, column 2 = % def…[Read more]

Tim Folkerts replied to the topic Regression Equatiuon in the forum General 18 years ago
Phil & TC:
I’d add a caveat to the caveat: “If you overfit, you MAY get a model that fits very well within the range of the data you have. However, you can also get a model that fits only right near the specific data points you have. Extrapolating (estimating values outside the range of your data points) will almost certainly work poo…[Read more] 
Tim Folkerts replied to the topic Control Chart for Growth Rates (percentages) in the forum General 18 years ago
In a business setting, I would tend to say that a control chart for growth rate wouldn’t make sense. To make a control chart, the first requirement is that the precess is “in control”. For most companies, growth is anything but in control. Every month it seems there is a new “special cause” of variation – a supplier can’t send a shipment…[Read more]

Tim Folkerts replied to the topic Excel and converting to time in seconds in the forum General 18 years ago
OOPS!
I got the numbers mixed around a bit. I was half way between doing it with the builtin functions and doing it from scratch. Faceman got it right!
{The other possibility is it do =A1*24*60*60 for the number of seconds since midnight}
Tim F 
Tim Folkerts replied to the topic Excel and converting to time in seconds in the forum General 18 years ago
Steve’s method using text functions is one method. You can also use time functions that are built in to Excel. (The real hardcore mathematicians can always do it from scratch, but that might be a bit much).
=SECOND(A1) returns the seconds since the last minute for a cell formated for time. Similarly for =MINUTE(A1), and =HOU…[Read more] 
Tim Folkerts replied to the topic confounding in the forum General 18 years ago
I find agricultural examples to be relatively intuitive, so let’s consider a 2 level factorial design. I should warn you, it’s kind of long….
Suppose you want to see what factors might affect how well plants in your garden grow. You choose several factors:
R: rototill the soil to loosen it
F: fertilize the soil
W: weed the garden regul…[Read more] 
Tim Folkerts replied to the topic DOE with continous factors in the forum General 18 years, 1 month ago
>Knowing simply that the response variable is airflow,
>I’m curious how can you conclude that all three factors are signficiant
>without collecting any data?Knowing simply that the response variable is airflow,
>I’m curious how can you conclude that all three factors are signficiant
>without collecting any data?Knowing simply that the…[Read more] 
Tim Folkerts replied to the topic DOE Help in the forum General 18 years, 1 month ago
Have you considered using some pattern to the selection of cavities, rather than just random?With 128 cavities, I would guess you have a 8×16 grid (although that isn’t critical to what follows). I’m no expert on molding, but I expect at least some of the variation is due to where the mold is physically located. For example, the temperature may…[Read more]

Tim Folkerts replied to the topic Inspection Plan in the forum General 18 years, 1 month ago
T.K.
I set up a little table, but basically the equation is the binomial distribution:
=BINOMDIST(0.095,30,0,TRUE)
The first number is the defect rate, the second is the sample size, the third is the number of defects found. The result here is 0.05006
By trial & error, I adjusted the first number until the result was down to 0.05 (i.e. t…[Read more] 
Tim Folkerts replied to the topic Inspection Plan in the forum General 18 years, 1 month ago
T.K.
It seems like a reasonable plan. Of course, it depends on what level of quality you are trying to achieve. A couple minutes playing with excel indicated that for each batch:
* you have a 95% chance of catching a lot with 9.5% defects.
* you have a 50% chance of catching a lot with 2.3% defects.
* you have a 5% chance of catching a lo…[Read more] 
Tim Folkerts replied to the topic Need help for DOE in the forum General 18 years, 1 month ago
Fernando,
To me it would be valuable to know more about your factors. As I see it (and please correct me if I’m wrong)…
You have 3 factors which you can control.
* Two choices of impellers which controls the flow rate. We could call this factor I 9for impeller), and it can take on the value I = (1,2)
* Eight choices of “flow distort…[Read more] 
Tim Folkerts replied to the topic Fitting a distribution conflict in the forum General 18 years, 1 month ago
Marty,Interesting. I have Minitab 14.1. I first ran it just using the Graph, Probabilty Plot, menu choice. It plots out the data with a fit to a distribution, along with some basic stats. Just now, I reran it with your method. The two results are indeed quite different. I also tried Stats, Basic Stats, Normality Test, and that gave the same…[Read more]

Tim Folkerts replied to the topic Fitting a distribution conflict in the forum General 18 years, 1 month ago
When I run the numbers in Minitab, I get much different results. First of all, a quick check using a histogram makes it look like the data set is not normal to begin with. There seems to be an unusual grouping near 0.035 and again near 0.045 The number I get are AD P
Normal 0.366 0.413
Weibull 0.341 0.480These numbers…[Read more] 
Tim Folkerts replied to the topic Am I using the right tool – right approach in the forum General 18 years, 1 month ago
Personnaly, I think Stan & Dr. Steve both have valid point. They aren’t contradicting each other, merely looking at different aspects of the same problem.If I might paraphraphrase…vb: “I can make great parts within a given run, but there is a lot of variation between runs. How do I improve the overall cpk.”Stan: “Consistency is a problem.…[Read more]

Tim Folkerts replied to the topic Sample size – should difference exceed std dev? in the forum General 18 years, 1 month ago
Suppose you were going to Las Vegas to play the new “Black Belt Slot Machine”. You know that the machines are designed to produce a payout with a normal distribution and standard deviation of $5, but the average for each machine may be different. It costs $100 to play. You play once and you get back $98.
Should you quit your machine…[Read more] 
Tim Folkerts replied to the topic AQL values in the forum General 18 years, 1 month ago
Gabriel,
GOOD POST. I think we pretty much agree, we’re just coming at it from opposite directions. Basically, sampling is a poor way to ensure quality.
As you point out I was analyzing various plans keeping AQL fixed. It could certainly be argued that keeping RQL fixed is a better idea. I chose AQL primarily because that is more fami…[Read more]  Load More