# confidence interval

1. ### How to estimate a population prevalence from several primary studies

I have received point estimates from several studies for the prevalence of a rare disease, and I would like to estimate the over-all prevalence in the population of interest, together with some indication of the precision of the estimation (preferrably a confidence interval). The trouble is that...
2. ### Ratio of Means - appropriate test for single or multiple comparisons? Fieller's CI?

I would really appreciate any suggestions with the following data analysis issue. Please read till the end as the problem at first may appear trivial, but after much researching, I assure you it is not. The situation is a little complicated because I want to compare the ratios of means: For...
3. ### Distributions and means - confidence interval question

Hi folks, :wave: I think I did my research but I would like to be sure before continuing. My task is to find the mean price of a given item in a given country and I need to know how accurate my sample mean is vs. the actual population mean. Here is what I have. (My proposed, probably...
4. ### Fitting confidence interval lines in R using the predict function

Hi everyone, I am currently attempting to fit confidence interval lines to a regression model in R, but every time I try to for example add a +2 confidence interval line, I end up with two of them! I have been over my code many times and can't find any obvious mistakes. This is the code I...
5. ### permutations and confidence intervals

Hello! I am in need of a little guidance on a stat problem... I've performed a permutation on two data sets, in R, regarding sunblock efficacy, and have concluded that in any permutation, there is only one instance of matching efficacy, the original data set. now I have to find a 95% C.I...
6. ### General Question Regarding Construction of Confidence Interval

Hi! I have a very basic question regarding confidence intervals. Given I want to construct a confidence Interval for the expected value mu of normally distributed Random Variables. As an estimator for mu I use the sample mean, \bar(X) = 1/n sum_(i=1)^n X_i that is. Now I want the real value...
7. ### calculating confidence interval bands for a normal probability plot

Hi I am producing a normal distribution probability plot, and I have a few questions related to confidence interval. An example of the plot I am creating can be found here: http://jsfiddle.net/jlbriggs/2gmtB/ Calculated based on the methods described here...
8. ### Mechanical Engineer, four cavity mold, how many parts to test?

My friend is a mechanical engineer at a company in CT. I was pretty good at stats back in my day so he asked me to solve this for him. This is a REAL question he is facing for his company/customers. There are 200(+- a few) parts in a bin. The parts were made from a four cavity mold. There...
9. ### Significance when self-selected participation is low

Suppose we have 1000 people. Of those 1000, 4 men and 2 women express interest in option A. Note that each one of the 1000 does not have to render a decision on option A, this is a self-selected scenario where only those who choose to express an interest do so (e.g., someone "like"-ing a...
10. ### Statistical analysis of Profits - use of U-test

Hi We have been working on a project where we have 2 or more trading agents on a market stock and for the outcome we have the profits that each trader generated after running 1000 times or more each market session. We need to statistically compare the profits of this traders to know which one...
11. ### Bootstrapping with One-way ANOVA design and confidence interval

Hello, I am new to this forum, and I need some helps in bootstrapping. I am using Matlab. So, here's the study design: I have three groups (Group1, Group2, Group3), 30 subjects/group each. They all have some brain imaging scans (FDG-PET). Within each group, I calculated some parameter...
12. ### (Binominal proportions) confidence interval – which formula to use?

Hey, I got a quick question regarding confidence intervals. For a Rasch analysis I have to perform independent t-tests (it’s done to check for unidimensionality). It is expected that 5% of these t-tests will be significant due to chance. Now I get 8 % significant and I want to see, whether 5%...
13. ### CI and Odds-ratios calculation for 2x2 tables.

Hi, I am currently trying to see if there is an association between a specific haplotype and and disease i two population. So far i have managed to do a Fisher´s exact test however i would also like to calculate the odds-ratio and see the CI if its possible. Using the command: tab rowvar...
14. ### Significance testing on share of spend

Hi all, can someone point me in the right direction for how i would work out stat sig of share of spend? eg - 5 companies in market, ask ppl how much you spend with each for say phone bill. This will then give total spend for each of the companies, and total market spend, therefore can...
15. ### Confidence interval, does a difference in sample size affect comparison of results?

I have a time series and im trying to calculate the confidence interval (95%) for the time taken to experience a +ive or -ive move of X%. I would like to do this for several X's, ie 10%, 30%, 50%. Am i correct in assuming that i should try and ensure that each level of X% has the same/similar...
16. ### How to calculate Confidence Interval from correlation latent factors in CFA?

If want to calculate the 95% CI of the interfactor correlations (correlations between latent factors) in a CFA, I believe I do this by multiplying the standard error by 1.96 and add/ subtract this from the correlation? However, AMOS only gives standard errors of the covariances, not of the...
17. ### Confidence interval from st. error when the mean must be positive

Hello all, (Statistical newbie here - learning some basic concepts) Some background (you can probably skip to the 'important bit', but just in case...): I am calculating the mean number of stratospheric sudden warmings (SSWs) per year. An SSW is a winter atmospheric event which happens...
18. ### Comparing confidence intervals: CI of mean vs CI of regression coefficient

Hi, I have longitudinal data with measurements at two timepoints. I am interested in the change per year and calculated this in two ways: * Dividing the difference between the measurements by the time difference and averaging over all cases. * Performing a linear regression with subject...
19. ### Null hypothesis

4. http://i42.tinypic.com/2woyqgz.png 10. A physician claims that as soon as his patients have a positive pregnancy test, he is generally able to predict the sex of the baby and that his probability of being right is greater than the one-half that would be expected if he were just guessing. A...
20. ### Uncertainty in Standard Deviation

The 95% confidence intervals for the standard deviation (SD) of 5 measurements is approximately 0.6*SD to 2.87*SD. The measurements are laser analyses to determine the atomic composition of a solid material. If each of the 5 measurements, stated above, actually consist of the average of 50...