Darth, You said, “Before this exchange gets out of hand, let’s forget what has been said and see if we can agree on a definition. A random sample is drawn from a population. A 95% confidence interval is calculated from the sample average, s.d. and size. What this means is that as we take more and more samples we expect that eventually 95% of…[Read more]
Darth,You apparently still don’t get it. I am not at all concerned about the 95 out of 100, but rather your misstatement of the meaning of a confidence interval. For a confidence interval constructed such as the one the original poster posed, about 95 times out of 100 the population parameter of interest will be contained in that interval. Your 4…[Read more]
So you still stand by your original statement? You are wrong. 95 out of 100 samples will NOT of necessity be in any other CI constructed. By your own post you do state the true meaning that the population parameter will be in 95 0f 100 such intervals constructed. You exhibit an arrogance which I did not think you had. I was hoping you would…[Read more]
Want to get into a semantics fight? Your statement,
“based on the sample, 95 out of 100 times a sample proportion will fall between .075 and .129”
is not quite correct.
I like the second statement much better.
It really doesn’t matter for most purposes, thought you might enjoy thinking about this.
“On the other hand the 95% confidence interval means that out of every 100 people surveyed (sample), 95 will have the true population value within the 78-72%.”
It’s a bit of a picky point, but your statement is incorrect. The meaning of a 95% confidence interval is that if 100 samples are taken, on average 95 will…[Read more]
Order of the data for Cpk is essential for individuals because the moving range is profoundly influenced by order and std deviation is estimated by control chart methods. If subgroups are used, this is not the case as range within subgroups is not order dependant. Ppk is not affected at all since the RMS std. dev. estimate is used.
To the…[Read more]
The formula your reference is a modification of the sample size formula for a mean in a normal population.
In order for your approximation to the normal to hold for the proportion it is neccessary that both pn and (1-p)n or qn are greater than 5. Given the sample size found (95) and checking the >5 criteria, you get p in the sample as…[Read more]
Power and sample size calculations for the Weibull distribution are complex particularly when the sample size is small. Monte Carlo simulation is best.
Take a look at: Lam & Spelt, “Comparison of Weibull Small Samples Using Monte Carlo Simulations”, Qual. Reliab. Engeng. Int. 2007, 23:503-513.
With all due respect, your statement:
“They think they removed outliers and the correlation got worse. The only reason that would happen is they were not really outliers.” ,
is not true.
They may have been outliers, and also be high influence points.
Model two columns of random integers. Get the corelation coefficient. Now model one…[Read more]
Chad, Do a little more study. You are still off track. Hint, zero correlation is inherent in the definition of independent variables. A zero correlation coefficient mean that no linear relationship exists. It does not imply that ANY other relationship exists whatsoever. It may be that a non linear relationship does exist and happens to have a zero…[Read more]
Your statement,”If your r value is close to zero, then you have a Non-Linear Relationship. Your data points on a scatterplot will appear to be in a U shape or vice versa.” is absolutely incorrect. Better scream some more. Otherwise good summary.
“Design and Analysis of Experiments” , Montgomery.
Covers 2 factor random and 2 factor mixed models, rules for EMS, CIs around variance components, approximate F tests and more. It’s chapter 11 in my copy (4th edition). Might be expanded in other editions, don’t know. I Googled and found 4th edition at B&N website used for around $85
Please repost with clarified numbers.
I think you mean LCL = 0.050965 not 0.50965. What is the sample size used to calculate these limits? I’m not familiar with a convention where we have significant digit comma two more digits comma three more digits? Is it six hundred thousand? Six million? Sixty thousand?
Your calculations of the…[Read more]
Dan, Why don’t you give us the ANOVA table? It would help to understand. When you say the one variance is 3 times the others, you do not indicate any statistical test of homogeneity. Was one done.The assumption of equal variance is because we are using that assumption to conduct analysis of the sums of squares between and within groups. With that…[Read more]
“However, the 3 requirements for implementing SPC are these: Clear specifications, a means of measurement, a method to adjust the process. Good luck.”What have clear specifications to do with it?Why would we need a means to adjust the process?I think you’re a bit confused, but perhaps I need the better understanding.
Darick,You are on the right track. There are criteria as to when you recalculate control limits. The advice from other poster is completely unsound. Find a copy of Wheeler, “Advanced Topics in SPC”, to see what to do. The basics are that you adjust control limits when there has been a shift, you know why, and you want to maintain the shift. Never…[Read more]
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