Search results

  1. Miner

    Seasonal Time Series

    You can find a lot of time series data sets at the US Census Bureau website.
  2. Miner

    Why is there a difference in the confidence intervals calculated by SPSS compared to SAS and Epi-Info 7?

    Also, some software offers multiple options for a given test and may offer a different default test. For example, Minitab offers three options for the normality test: Anderson-Darling, Ryan-Joiner and Kolmogorov-Smirnov, with the A-D test as default. If another SW package set K-S as the...
  3. Miner

    Why is there a difference in the confidence intervals calculated by SPSS compared to SAS and Epi-Info 7?

    Have you tried going to each company's website and looking up the CI formula used?
  4. Miner

    3-way ANOVA with two significant 2-way interactions

    That is not necessarily true. The best improvement may indeed be in older males based solely on those two interactions. As Karabiner stated: "Interactions are differences of differences." A 3-way interaction would simply mean that the improvement due to gender and the improvement due to age...
  5. Miner

    I am running a regression analysis and I´m not sure what data I should use

    I would start with scatter plots to determine what relationships might exist, and whether there are any outliers that might influence the correlations for the better or the worse. The plots would also show whether any relationship is linear or not.
  6. Miner

    I am running a regression analysis and I´m not sure what data I should use

    It depends on the question that you are trying to answer. You can do a regression either way (or on standardized values), but the model and the coefficients mean different things. Decide on the question and match the regression to answer that question.
  7. Miner

    Generalized linear mixed model: Type III significant but multiple comparisons not significant

    You can run another experiment with the two most likely candidates and test those separately.
  8. Miner

    Generalized linear mixed model: Type III significant but multiple comparisons not significant

    Another issue is that when you run multiple comparisons, the test (say Tukey's) places a fairly high hurdle to pass to demonstrate significance. This is because when you test all possible combinations of treatments you increase the risk of a false positive. If you were to have an a priori...
  9. Miner

    Mean time between failure caused by natural death

    Is this a product reliability issue? If it is and I understand your explanation correctly, there are two ways to deal with this. One would be to use only the failures due to the failure mode of interest and treat all other failures as right censored data. This will provide you with...
  10. Miner

    Contributing factors within ANOVA

    Try Dunnett's test. It is designed to test experimental treatments against a control.
  11. Miner

    drawback of hotelling t2 statistics

    I suspect that the OP means Hotelling T2 control charts. My understanding is that they are a multivariate control chart that is intended to provide a signal if any one or combination of variables changes in a process. I have never used them, and am only aware of them on a theoretical basis...
  12. Miner

    HR Salary analysis

    You should also consider interactions between variables and other factors such as length of time with this organization. In many organizations, people that switch jobs between organizations and within the organization will earn more faster than people that stay in the same job and same...
  13. Miner

    Paired-T or Independent T?

    It depends on whether the samples are dependent or independent of each other. If there is some form of dependency between the samples use a paired t-test. If they are independent of each other use a 2-sample t-test. In your case the only way that I can see a possible dependency is if on each...
  14. Miner

    P charts based on binomial distribution - Statistical Process Control

    The article "Are you sure we don't need normally distributed data?" by Dr. Donald Wheeler provides additional support to Deming's assertion. I have found Dr. Wheeler to be an excellent "go to" resource for industrial statistics. "Myths about process behavior charts" is another good read.
  15. Miner

    P charts based on binomial distribution - Statistical Process Control

    One final note that may help you understand the greater issue. This concept has been mistakenly taught for decades. Control charts are NOT statistical tests. They are EMPIRICAL tests. The control limits were empirically determined to strike an acceptable balance between the economic costs of...
  16. Miner

    P charts based on binomial distribution - Statistical Process Control

    Welcome CedricLVQ, As a preface, you were fortunate to get the attention of one a very small number of people that would have a clue about a p-chart. There are two other forums that specialize in quality topics, including SPC. The largest one is the Elsmar Cove, and the other one is Quality...
  17. Miner

    Probability of Energy Shortage

    I used Quantum XL. It is an Excel add-in, and is currently priced at $549 USD. This link has a step-by-step for Minitab. While there are some Minitab-specific instructions, the actual steps are fairly generic. There are also a lot of YouTube videos that may be helpful.
  18. Miner

    Sample size for destructive testing

    Are the results in the form of a continuous measurement, or a binary pass/fail? Do you have any historical information on the variation of the process? If (and that is a big if) you have historical data that indicates that all of your process variation is at a comfortable distance from your...
  19. Miner

    Probability of Energy Shortage

    The easiest way that I could come up with was a Monte Carlo simulation using your empirically derived distributions. I came up with a probability that demand would exceed capacity approximately 0.55% of the time.
  20. Miner

    Normal Distribution?

    The correct term is bimodal. Try finding the factor(s) that explains why there are two distinct groups. That may or may not be a factor within your control (e.g., starting a family and needing a larger place) . If it is in your control, use it to move more from one group to the other. If it...