confidence intervals

  1. M

    Confidence intervals exceeding 100% and going below 0% for mortality rates

    Hello, This is probably a very naïve question however, when plotting some graphs of mosquito mortality against different insecticide treatments I noticed the confidence intervals for some of the most effective treatments exceed 100% and that in the control they sometimes go below 0%. Firstly...
  2. M

    Why One Sample For Confidence Intervals?

    As I understand it, The Central Limit Theorem and Confidence Intervals are related. What is the best way to explain why the Confidence Interval formula uses only one sample whereas the Central Limit Theorem uses 'many' samples? Isn't the x-bar in the CI formula the mean of one sample? Don't we...
  3. G

    Construct a 95% confidence interval for the population proportion of all students...

    A researcher wants to know what proportion of all students who have completed a course in Statistics do not have a solid understanding of what a Sampling Distribution is. A random sample of 320 students who recently completed a Statistics course were given a basic exam on Sampling Distributions...
  4. T

    Confidence Intervals. Why Just One Sample?

    A typical problem in a Stat Textbook for creating a confidence Interval sounds like this: A sample of 50 blood pressures is taken and the sample has a mean of 120 with a standard deviation of 5. Construct a 95% confidence interval. What troubles me is that only one sample is enough. Intuitively...
  5. R

    Bayes - need help informing priors

    Hi! Anyone here familiar with Bayesian inference? I would like to inform priors for an analysis. I have Odds Ratios and 95% CIs. How would I calculate the variance from the CIs. I know how to calculate SEs, but I don't think that is the custom for priors (its usually mean and variance)...
  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. A

    Large Sample Confidence Interval for the Mean - Problem is it right ???

    The president of Jones Bank asked his research team to determine the average waiting time for its customer. A study of 100 customers was conducted with the following results: mean = 19.8 standard deviation = 2.06 minutes Prepare the 95% confidence interval for average waiting time... mean =...
  8. C

    Equivalency testing - CI approach and TOST don't match

    Hey everyone, I'm doing some equivalency testing with both the CI approach and TOST to demostrate the equivalency of two scanning methods. For most of my samples, results align as one would expect, i.e. if the CI lies within the upper and lower bounds, the p-values calculated with two...
  9. L

    Confidence Intervals in a research paper

    Hi, all. I'm writing a paper on concussion data from the NFL Surveillance System, and I want to be able to put the data analysis from the journal article in my own words, but I don't really understand what the researchers are saying. Here's the quote. Can someone please tell me basically what it...
  10. P

    False Coverage Rate - adjusting confidence intervals for multiple comparisons

    Hello, I could do with some help regarding correcting confidence intervals for multiple comparisons. I have carried out a number of multiple regression analyses, which has given me various different p values. I have used the Benjamini Hochberg procedure to determine which p values survive...
  11. T

    please help me justify sample size for a pilot clinical trial

    I'm a bit desperate for statistical help so trying out all avenues. Any guidance appreciated! I need to justify a sample size of 30 or 32 (15 or 16 per arm) for a placebo-controlled pilot clinical trial of a drug. This is all I can afford, but that is not a good enough justification for...
  12. R

    Data analysis

    I have been asked to analyse the following data using linear analysis, mean standard deviation and ANOVA. However the data presented is supposed to be continuous but for small values they have grouped them as less then 5 almost like discrete. They represent the ages of children using...
  13. P

    Inaccuracy of Non-Parametric Bootstrap for great sample sizes in Excel-VBA

    My aim is to evaluate the performance of parametric and non-parametric Bootstrap under specific circumstances; and particularly their ability to capture the population mean within their produced confidence intervals -from now and on when talking about "coverage" I mean the ability of the...
  14. K

    confidence intervals for correlations on AMOS or SPSS

    Hello, I was wondering how to calculate confidence intervals for a correlation coefficient on Amos or SPSS. I've been trying to do it on SPSS by standardizing my data, but i've been told the estimate is not fully accurate. When i try to do it on Amos, i get the correlation coefficient but no...
  15. K

    Trimmed Spearman_karber Method using r for dose response analysis - Help needed!!!

    Please could anyone show me how to go about using r to LC50 and Confidence intervals with Trimmed Spearman-Karber method? I have had several go at the codes provided online (e.g, shown below) but couldn't make any progress. I loaded the package "drc" on r and yet couldn't find my way in using...
  16. D

    Confidence interval for person time incidence rate

    Dear everyone, I would like to estimate a 95%CI of person time incidence rate (as 45 death per 10,000 person year) Anyone knows a way to estimate it ? Same question for Kaplan Meier estimate.. Thanks a lot for your help!
  17. J

    Confidence Interval homework help

    This is the only part of our homework I am not understanding... A.)If the 95% confidence interval for the population mean is (6,20), what is the sample mean? B.)Given the 95% CI in part a, would (5,21) be a possible 99% CI for the same sample of data? If not, why not? C.)Given the 95%...
  18. D

    Pearsons correlation, confidence intervals, bootstrapping... Statistical nightmare

    I am currently running a project where I have 4 variables and a questionannaire with 4 subscales. I have performed a Pearsons correlation on this (due to high frequency of extreme scores in the questionairre and non-normal distribution of the questionnaire) and have found 2 significant results...
  19. K

    Multilevel meta-analysis in R using lme4 and lmer

    Dear users, I am running multilevel meta-analyses in R using lme4 and lmer. lmer(effect size ~ -1 + Covariate + (1|StudyID), data = data, weights = weights) My question is – is there a way to calculate confidence intervals that takes into account the fact that some effects are nested...
  20. F

    How to calculate the confidence interval of the ratio of two means (paired data)

    Hi there, I am writing a systematic review and need to calculate the 95% confidence intervals of the ratio of means from whatever the clinical trials I'm reviewing give me. The problem is: none of the studies actually report this information, and all I am given usually is the mean...