confidence intervals

  1. J

    Confidence intervals: normal vs t-distribution (central limit theorem)

    Hi all! We did a serological survey for a disease taking 300 samples in a population of 50 000. If our sample mean gives a 2% prevalence. How do we work out the confidence intervals? I have all the formula's and there are great CI calculators on the web BUT seeing that is only one survey...
  2. A

    help!! I have a test and none of this makes sense.

    Hello! I have an exam on inferential statistics, etc and need serious help.
  3. M

    Reaching a 95% Confidence level within an estimated population.

    How can I reach a 95% Confidence level after estimating the population size? I have a population of 367 products of which I have a sample of 50. Products can have a damaged package or can be damaged itself. We know for a fact that products can only be damaged if the package is damaged. From the...
  4. M

    Non-Parametric Analyses. Report medians and 95% CI in graphs?

    Okay so, I'm currently writing my thesis, and I have to do non-parametric tests. I know that I have to report the medians in text. However, I'm doing graphs. Just wanted to ask whether anyone knows if I report the 95% CI and the medians in the graphs? When i do this it looks super weird and...
  5. H

    Probability that Bernoulli p-parameter is greater than some value, given N samples?

    Hello everybody, I have the following question. Assume I observe N outcomes from a Bernoulli random variable with unknown success parameter p. Based on these outcomes (or samples), how likely is it that the real parameter p is larger (or smaller) than a given value eps (e.g., 1%)? Any...
  6. C

    Clarification on Error Propagation

    I thought I understood the basic operations for error propagation (addition, multiplication, etc), but I have a few questions: 1. Is variance the only measure you can use? I only have 95% CI available to me. 2. Does multiplying/dividing a mean +/- CI by a constant preserve the error (ie CI...
  7. M

    Confidence intervals for eta squared?

    Hello, is it possible to calculate confidence intervals for eta-squared manually? I found a paper which lists the formula for this: http://www.jstatsoft.org/v20/i08/paper (pages 12 and 13), but the paper doesn't say how to calculate ^L and ^D, which are a part of the formula. Can anyone please...
  8. O

    Help with confidence interval and interpreting data!?

    Someone please please help me make sense of these stats! I really need help with interpreting outcome of studies! How do i calculate CIs (no need to know actual calculation as can use calculator) and make sense of outcome... Any help would make me forever grateful! STUDY 1. Pre- and...
  9. A

    Determining an indirect confidence interval for justifying a non-inferiority margin

    I need to establish the efficacy of a test treatment (T) by means of an indirect comparison to placebo (P). Therefore a study of T vs. reference (R) will be performed, and there is 'historical' data for the comparison between R and P. The outcome measure of interest is a responder rate (i.e...
  10. D

    Does Sqrt of confidence intervals require a correction factor?

    I have the following formula for confidence intervals on samples from a Rayleigh process: \frac{2(n-1)\overline{r^2}}{\chi_2^2} \leq \widehat{\sigma^2} \leq \frac{2(n-1)\overline{r^2}}{\chi_1^2} I want to give confidence intervals in terms of \sigma, not \sigma^2. If [x, y] are the 95%...
  11. H

    Need help: Can i genaralize to the population, or do i have to weight my data?

    I have a sample of 194 households from 3 villages. The number of hh from each village is 61, 67 and 66. I used a 90% confidence level and 10% margin of error to determine sample sizes. (total household population for all three villages is 4194 households). The total sample size for all three...
  12. M

    95% Confidence Interval for Regression Coefficients Question

    Hello all, I have been trying to figure out how to answer these homework questions for far too long and happened upon this forum with hopes that I could get a nudge in the right direction…Here is the problem as an attachment. Also included is my work thus far…I think my issue is...
  13. N

    Confidence Intervals for r: Why must we standardize?

    Hello! I know we are supposed to convert our r-values to z-values (and standard error) in order to calculate confidence intervals. I am a bit confused why we must do this. The sampling distribution for Pearson's r is a t-distribution and we use a t-crit in confidence intervals when our N...
  14. P

    [SaTScan] relative risk confidence interval calculation

    Thank you for reading this. My question is regards the methodology used by SatScan for purely temporal cluster analysis using a discrete Poisson model satScan's output gives me the following: How do I calculate confidence intervals around the relative risk? Thank you!
  15. T

    Accounting for confidence intervals in determining a mean

    I have received some elemental analysis of a metal which I want to use to determine the effects of radiation. I want to report my results for the mean and 90% CL. The analysis only presents 8 data points for each element so I was planning on using the t distrobution as follows...
  16. M

    Statictics Assistance needed

    Hi Im really stuck with a particular question regarding calculating confidence intervals. I dont expect anyone to solve it for me but just a push in the right direction would help heaps :) Recent research published in the Proceedings of the National Academy of Sciences has examined whether...
  17. S

    Is there a test to see if a sample (one result, many parameters) is an outlier?

    I am posting here because I am not sure really how to look for my answer. I am used to comparing means of two samples, but what happens when you have only one sample but 20 parameters? How do you determine if this is significantly outside the data cloud for a data set that has about 100 samples...
  18. V

    Using the Right Test to Confirm Separation of Confidence Intervals

    Hello, I'm working on a research project (not homework) and I could benefit from a quick consult since some of my stats are a bit rusty. I have a series of experiments that qualify as Bernoulli trials, so I am estimating 95% confidence intervals on the success rates assuming the binomial...
  19. S

    Confidence limits for logistic regression equation

    I have generated a logistic model for a disease status Y (unaffected-affected) using several independent variables on a very large (600K+) dataset. I then want to apply that formula to a much smaller subset of that data set, having a particular characteristic not included in the model. I then...
  20. W

    Trying to evaluate/measure how much 1 variable affects another.

    Hello. So I've been helping look at some data for a fundraising event my school ran. We used an app and the school wants to evaluate if it is worth it. From the event I have the data of all donations (how much it was and who it went to). So what was done is for all fundraisers the sum of all...