# Search results

1. ### Real world measure - Emergency Services

I created a variance-covariance matrix as well as the correlation matrix, and the data seems to be independent (meaning looks random). May I suggest looking at other factors that are not times that are used in the calculation of the 'Time to Scene". Also, comparing the hits to miss may give...
2. ### Proportion Z-score calculator

The normality assumption is usually reserved for when npq >= 10, where q = 1-p. That's my rule of thumb at least. When you get very high/low p's the distribution is less normal and exact calculations are preferred. I think the way to go about this is to create confidence intervals of p for both...
3. ### Sensitivity and specificity

I assume you have historical patient data with tests A and B and the presence of the condition? Assuming the population is not biased in any way, you could just compare the spec/sense of A alone and B alone. You could use Youden's J Statsitic for informedness (Spec + Sense - 1) to see which test...
4. ### Probability 2-vector probability

English translation available?
5. ### Standard Score (z-score)

I think the conceptual point of interest is that any normal distribution and be transformed into the Z (Standard Normal) distribution. In you thinking of transforming by using a*X + b; a = 1/sigma, and b = mu. Because the E[X] is mu, the b term is not "dependent" on X the way you are thinking.
6. ### Difference of Means

That 1.64 makes sense that you are conducting a 2-tailed T-test. Essentially by using that you are splitting your alpha risk between the m1>m2 and m1<m2. Using the 1.64 accounts for both, so in essence you are checking for both.
7. ### Calculate propability of certain outcome

First lets address the testing of 100 people and finding that 3 have it. 3% is your estimated prevalence of the disease, not the true prevalence. You would need to test everyone, or a massive amount of people, to come up with an accurate population prevalence. Next, using this estimated...
8. ### Difference of Means

Are you conducting multiple pair-wise tests? If so, you are exposing yourself to more alpha risk than just 0.10. If you are comfortable with 0.10 alpha risk then you will need to adjust your individual test's alpha to give the entire projects risk of 0.10 . Lets say have 1 control and 5...
9. ### Difference of Means

You are conducting a 2 Sample T-test with unequal variances, is that what you want to do? This is only valid if there is 1 control and 1 treatment group. If you have multiple treatment groups then an ANOVA would be more appropriate.
10. ### Help selecting test

You just conducted a 1-Sample T test and you didn't even know it. You essentially gave evidence that there is a difference in scoring between a non-trained person and a vet in the first one. And in the second one you again gave evidence to show a difference in the scoring on a trained person and...
11. ### Help selecting test

Okay, so the 1-9 scale is ordinal data, meaning '1'<'2'<'3'<...<'9' but it does not mean a cat with a score of '6' is twice as good as a cat with score '3'. A T-test is used on continuous data like time, length, etc. where there is an infinitely amount of possibilities. Also, let think about...
12. ### Help selecting test

How are you measuring the end result? I think a little more information about how you are measuring will help us lead you to the correct test. Also you mentioned a professional opinion as the 'correct value'. I think you might be interested in two things, the training's impact on getting closer...
13. ### Infer confidence intervals of MLE using fisher information

I have some count data that looks to be Poisson. After a goodness of fit, chi-squared test with p=0.5, I am comfortable saying it is from a Poisson distribution. I want to get confidence intervals for the mean/lambda. Can I use fishers information to find the variance of the MLE, and then use...
14. ### Help with poisson

Poisson is a distribution the has probability masses at 0,1,2,3.... infinity, where all the masses sum up to 1. What you are looking for, I think, is a prediction model. I would first start with the question of, "does a previous score depend on the current score?" You could build a 3x3...
15. ### PPM calculations for 6 Sigma

Ramkiran, You first need to understand the difference between Cp and Cpk. Cp (Capability of the process) only describes the variation of the process in respect to width of the specs, regardless if it is centered within specs. Cpk(Cabibility of the process katayori {katayori is Japanese for...
16. ### Why is there n-1 degrees of freedom and not n-2 (student distribution)

Rafaelle, you are not having to guess the variance at the same time as guessing the mean. Think of the data points creating the hyper-plane of n dimension covering all possibilities of data. Then the mean and variance in this case can have all possibilities in a 1 dimensional vector in this...
17. ### Why is there n-1 degrees of freedom and not n-2 (student distribution)

I may be able to add some clarity if you are familiar with MLE (maximum likelihood estimator) methods. In the process of finding the MLEs of a normal distribution (which the CLT [central limit theorem] tells us a sampling distribution converges to) we are looking to find the mean and variance...
18. ### Fisher Matrix and Parameter Confidence Interval

Thanks for correcting me on those. The variance of the product can get quite complex, this should be fun.
19. ### Fisher Matrix and Parameter Confidence Interval

I am working with some data that fits a gamma distribution and would like to get confidence intervals for the parameters alpha and beta. I have found the general form for the fisher information matrix of a gamma here and have the inverse to get the correlation matrix, but was wonder about how to...
20. ### Mean, Standard Deviation, and z-Scores...Oh My!

The theory here is that you can transform your observed data into a standard normal distribution, Z. Remember that the Z-dist has a mean of 0 and a standard deviation of 1. Z-Scores: These are how far away a point is from the mean. A Z-score of 0 is at the mean. Z of -1 means its 1-standard...