confidence interval

  1. Q

    P values from 95% CI using poisson distribution

    Hi, Hope I'm in the best place for an answer :) I have a study across 10 years. I have an incidence rate that was calculated for each year along with the 95% confidence interval using a Poisson distribution. My question is how do a get p-values for pairwise comparisons? I understand I can say...
  2. R

    Confusion between z and t values

    Hi, Alright so I have some confusion on when to use specific tests and the z vs t test. Given this example (not my homework) could someone please clarify. Alright say you have a random sample of size 200. You find the sample mean to be 10 and the sample standard deviation to be 5. What...
  3. J

    CI to percentage change in ICC

    I'm running fixed effects models to estimate changes in intra class correlations. I first run an unconditional model and then a second model including only level-2 factors. I'm interested in the reduction of the icc when adding only level-2 factors. I'm interested in expressing the...
  4. T

    Question about degrees of freedom in an independent sample t-test

    I've been asked the following question by a scientist who is not a statistician: Suppose we take a sample $x_1,…,x_n$ from a population that we can assume is normal (I don't think this assumption is critical). We then calculate the sample mean $\bar x¯$ and variance $s^2$. We then take a...
  5. E

    Overlapping confidence intervals

    Say I have a calculation model, calculating the a mean (lets say 36) value (with +-2 95% CI) as uncertainty for the calculation result. Then I measure the value 6 times, to a mean of 33 with (+1.5 95% CI), so the CI overlaps by .5 I want to say something about the compliance...
  6. S

    Can someone please check my answers? It's over confidence intervals

    This isn't techinally homework. It's extra practice questions giving by my teacher. I just want to make sure I'm understanding everything correctly. If I have a question wrong, can you please give me the right answer and explain it in great detail? 1. Construct a 95 percent confidence...
  7. K

    Measuring the effect of in-store Promotions

    Hello, I am testing the effect of a new in-store promotion technique (treatment). It is applied during product promotions, as a compliment to regular promo displays, to further improve sales. I have the treatment in only one store but on several products promotions in that store (I have...
  8. A

    Help with figuring out confidence interval level

    Hello. My group was conducting a statistics study and we had all our data in an Excel file. We held a pretest (asked survey to nonmembers of the population but had the same characteristics). The results that we got from there was what helped us determine the needed sample size from the actual...
  9. M

    Confidence interval: true or false?

    We have measured the concentration cesium-137 in the tissue of 15 tunafish. We may consider the distribution as normal distribution and a 95 % Confidence Interval for the mean concentration was calculated to (5.03 to 6.71) (Bq/kg). Is the following statement true or false: "The interval means...
  10. R

    Exp(B) or CI values with the letter "E"

    Dear all, I am running a Multinomial Log. Regression. Everything seems fine but I do not understand when Exp(B) oder CI values are like 1,000E-013. I see this result although, the goodness of fit of the overall model is appropriate. For example in: B=-107,4, p=0,031 Exp(B)=1,000E-13...
  11. M

    Can you use the same data twice to construct a confidence interval?

    A while ago I was asked the following question: What is with a 95% probability the maximum number of defects, given a population of size N=800 of which we inspected n=100 and found k=0 defects. I constructed a confidence interval based on the assumption of a binomial distribution and gave...
  12. P

    Lower/Upper confidence limits for 5/9 point rating scales

    If you have a rating scale such as are used on product websites where users enter scores 1,2,3,4,5 (five values) and averages are (presumably) rounded to discrete intervals 1,1.5,2,2.5,3,3.5,4,4.5,5 (nine values), what is the best method for calculating lower and upper confidence limits around a...
  13. E

    Trouble in interpreting the C.I for AUC using SPSS

    I calculated AUC using SPSS and the output was: 0.623, std.Error=0.056. p=0.055. lower Bound was 0.513 and upper was 0.743 How could it be that the p value is not significant and the lower Bound of C.I was more than 0.5? Am I missing something? Thanks
  14. C

    Author's interpretation of Odds Ratio and Confidence intervals

    Hi all, Having some difficulty understanding the results of this paper I am including in a review. It compares the effects of 3 interventions aimed at preventing HIV on couple's relationships. A multivariate logistic regression is used and effect estimates are given (which we are told are odds...
  15. D

    Generating confidence intervals for both height and weight with the same sample?

    Given that height and weight tend to be correlated, would it be okay for me to use a single simple random sample of people to create confidence intervals for both their height and their weight?
  16. J

    Please help interpret cross-sectional study results (odds ratio, relevant risk, etc.)

    I'm trying to help my wife with some statistics. She's looking to see if people with Removable Dentures (RD) have a higher prevalence of Combination Syndrome (CS). She did a cross-sectional study (survey) of 314 patients at her university. Of the 314 patients surveyed, 200 had Removable...
  17. J

    Confidence interval for Cohen's H

    hi everyone, I would like to create a Forest plot for a number of studies that looked at proportions. I calculated effect sizes using Cohen's H, but now I need to know the confidence intervals for those effect sizes. Does one of you know how to calculate those? Thanks in advance!
  18. F

    Confidence Intervals for Proportions -- Two ways to estimate population value?

    Hi everyone, I'm wondering if anyone could help shed some light on why there appear to be two different ways that different textbooks show to calculate confidence intervals for proportions. Within the formula I know, there is P, which is the population parameter/value we are trying to...
  19. K

    Confidence intervals from glmer models

    Hi! When reading this, please keep in mind I'm pretty bad with statistics so please bear with me. So, I'm trying to analyse data from an ecotoxicological experiment. I have fish that were exposed to a substance during development and want to look at behavioural effects in the adult fish. I have...
  20. A

    Kaplan meier: hazard and 95CI

    I have conducted a time to event analysis with the kaplan-meier method and my instructor requested for HR and 95%CI of specific time points such as 1 year or 3 years. However the life table in Kaplan-Meier analysis lists me the cumulative survival for time points at which last follow-up occured...