confidence intervals

  1. S

    Confidence Intervals for Pairwise Independant Normally Distributed Samples

    Good day, I have been thinking over this exercize for a couple of hours now and I have trouble finding a starting point. Suppose that X1,i iid∼ N(µ1, σ²), X2,i iid ∼ N(µ2, σ²), that the samples are pairwise independent, and that σ is known. Derive a 1 − α confidence interval for µD = µ1 − µ2 I...
  2. J

    detection rate question

    Hi, I have sort of a backwards question. I have a calculated detection rate and its standard error, and I know the number of positives that were detected. I am trying to calculate the total number of positives (detected and non-detected), and a 95% confidence interval for that estimate. The...
  3. D

    Confidence intervals, proportions

    A simple random sample of 1000 New Yorkers finds that 87 are left-handed. (a) Find the 95% confidence interval for the proportion of New Yorkers who are left-handed. The answer my professor gave and the answer that I got are completely off from each other. Here is what I have so far n = 1000...
  4. K

    Comparing two methods to measure disease severity

    I am testing a new, fast method to score disease severity in an animal model of a human disease. M appears to be less sensitive than the gold standard scoring method, G. G is discrete and has a range (0,1,2...20). M is continuous and varies from 0 to 1. The linear correlation coef between...
  5. A

    Summing Confidence Intervals?

    Hello, I have calculated mean concentrations of various environmental chemicals in a population. These chemicals fall into different classes (PCBs, dioxins, etc). There is a 95% CI associated with each mean concentration. I want to sum the mean concentrations for the chemicals in each class...
  6. E

    Need Help interpreting SPSS results- is level of effect significant?

    In my design, I have 3 binary items for each condition (4 conditions total) meant to measure the same thing. All participants were in all conditions (repeated measures, 12 scores each). I made a composite score for each participants for each condition (yes, I know, not advisable but this is...
  7. G

    Need Stats Help! Please!

    Two independant random samples were taken at two neighboring high schools to determine the difference in the proportions of students who had jobs outside of schoo. The sample of 75 North High students indicated that 60% of them had jobs outside of school while the sample of 40 south high school...
  8. X

    How to use instrumental variable to estimate hazard ratios and 95% CI?

    Hi, I am doing a Mendelian randomization analysis, by using an instrumental variable (Z, which is the genotype of exposure variable X), to investigate whether there is a causal association of genetically determined X on survival (Y). Suppose that Y includes information of both a dichotomized...
  9. B

    95% Intervals

    I'm new here (and relatively new to statistics) so I apologize if this thread is in the wrong place. I have a problem that seems relatively easy but it has me stumped... I need help with intervals on data. I thought tolerance intervals would work but they are not giving me what I want...
  10. N

    Question regarding confidence intervals

    Hello, Let's assume that we have two parameters A and B, for which a mean value (mA and mB respectively) is estimated over 100 simulation runs, each run using different random streams. A 95% confidence interval is evaluated for mA and mB, with a half-width of less than 5% of each...
  11. P

    Research question - How relevant is standard error/confidence interval in my case??

    Hello I work for an organization that has sent online survey requests to all of our clients this year (560 only from 2011). The response rate has been 51%. Because the sample is not random, but rather, "email sent to all clients"... Is it valid or just pointless to include confidence interval...
  12. J

    [Post Hoc Tukey Repeated-Measures T-Test] Interpreting results & Confidence intervals

    This has been solved using SPSS
  13. R

    Confidence intervals on a product of two confidence intervals

    I hope you can help with a practical problem I am facing. I have to estimate how much work will result from future business when our pilot system goes fully live with a hugely increased user based. I have used the pilot figures to estimate the average daily VOLUME of each type of task per...
  14. CB

    Bootstrap bca confidence intervals for large number of statistics (boot)

    (This isn't really a question thread - I'm just providing some possibly useful code, and asking for suggestions on how it can be improved). The boot.ci function in the boot package allows users to get confidence intervals for particular statistics, with the limits obtained via bootstrapping...