confidence interval

  1. V

    Cox regression survival analysis

    Hi, I am currently undertaking my dissertation and wondered if you could help me with some data analysis from one of my studies. The study indicates that they use Cox regression for survival analysis Results indicate that for group differences in depressive episodes the hazard ratio =0.38 95%...
  2. C

    Calculating the amount of underestimation

    Coverage rate for a parameter is 91.2%, and the nominal coverage rate is 95%. If the confidence interval is based on asymptotic standard normal, then the amount of coverage 91.2% implies that the standard errors for the parameter is estimated about 15% too small. Because z* value used to make a...
  3. G

    Sampling Protocol and Relative Sampling Error

    I’ve been racking my brain over what is likely a straightforward problem, but a little different than what I’m used to dealing with. I’ve got a sampling protocol I need to hit that states ”Confidence of the estimate should meet or exceed +/- 10% at one standard error”. I’m accustomed to...
  4. D

    Sample size - have searched high and low,bu tprobarbly very quick and easy to answer!

    Hello Friends, I haven’t looked at a statistics book for a good 5 years, since leaving uni and moving into the job world. However, I have come across a real world problem where I feel there is a statistical method to help me, but after searching high and low cannot find it. I’ve looked at...
  5. K

    Non-para: "THE CONFIDENCE INTERVAL FOR MEDIAN BASED ON SIGN"

    So my professor decided to write his own textbook, and we are finding errors everywhere, and it's difficult to understand, so I've tried google-ing and everywhere I go people are using different methods than the one he wants me to use here is an expample of what I am working with: 9. A...
  6. D

    Comparing a Binomial and Normal Distribution

    So I'm currently analyzing several sets of data, that all represent the exact same type of data. There are multiple sets of this data, but however are in different forms. That is, some of this data is in the binary form, either presence of absence, while others are in the quantitative form. My...
  7. C

    How is the confidence interval for variance component in "lmer" function computed ?

    Here is the R code : library(lme4) fm1 <- lmer(Reaction ~ Days + (Days | Subject), sleepstudy) confint.merMod(fm1,oldNames=FALSE) And the output is 2.5 % 97.5 % sd_(Intercept)|Subject 14.3814761 37.715996...
  8. C

    Confidence interval of parameters of mixed-model in R

    Hi , can anyone please explain me the following output produces in `R` when I ran the command `confint(lmer())` . Here is the R code : library(lme4) fm1 <- lmer(Reaction ~ Days + (Days | Subject), sleepstudy) confint(fm1) And the output is : Computing profile confidence...
  9. R

    Confidence level and Margin of Error applied to Satisfaction surveys

    Hello, New to the forum, relatively new to stats as well! So I think I've managed to confuse myself and am going around in circles with this, so help would be appreciated. I'll outline what i'm trying to achieve and what data I have available below: So, i'm sending out satisfaction surveys...
  10. 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...
  11. P

    Deducing Sample Size from Sample Proportion CI

    How do I approach this problem? Suppose we want to estimate a sample proportion to within 0.05 with 95% confidence, how large will the sample have to be? There is no other information about the distributions of the population or the sample. No point in trying to solve for n in the...
  12. A

    how does stata calculate confidence intervals for age standardised means/proportions

    Dear Stat Talkers! I'm using the following Stata command (see help mean): mean x, std(a) stdw(b) over(c) to get age-standardised mean or proportion of a variable of interest x. a= variable for age-group and b= variable for weights for each group. x can be a continuous variable or a...
  13. T

    Calculating observed probability

    Can anyone point me towards the formula and extra reading I would need to calculate how many observations I would need to make in order to calculate an observed probability within a set confidence interval? So for example, to calcuate how many times would I need to toss a coin to observe that...
  14. E

    Syntax and formula for the 99% confidence interval for a proportion

    According to: https://www.mccallum-layton.co.uk/tools/statistic-calculators/confidence-interval-for-proportions-calculator/ The 99% confidence interval for 23 out of 125 is: +-8.93, where observed proportion is 23/125=18.4%. When I try and replicate this in Stata, with reference to this...
  15. C

    Confidence intervals with a skewed histogram

    If a histogram is skewed right, does that give us any concern about the validity of a calculated confidence interval?
  16. M

    When to use which statistics? Is it correct like this?

    I never had statistics in school and I'm not in college yet so I try to teach in to myself now. That's why everything I write now could be plain wrong: - You use hypothesis tests (independent t-test, paired t-test etc) to test a claim about a population mean/population proportion or to test a...
  17. E

    Negative Confidence Interval

    3. In two wards for elderly women in a nursing home the following levels of hemoglobin were found: Ward A: 12.2, 11.1, 14.0, 11.3, 10.8, 12.5, 12.2, 11.9, 13.6, 12.7, 13.4, 13.7 grams/dl Ward B: 11.9, 10.7, 12.3, 13.9, 11.1, 11.2, 13.3, 11.4, 12.0, 11.1 g/dl Ward A Ward B n = 12 n =...
  18. E

    Confidence Interval

    In 22 patients with an unusual liver disease, the plasma alkaline phosphatase had a mean value of 39 IU/l (International Units per liter), standard deviation = 3.4 IU/l. Calculate the 95% confidence interval for the population’s true mean value of plasma alkaline phosphatase. My equation...
  19. E

    Confidence Interval

    In 22 patients with an unusual liver disease, the plasma alkaline phosphatase had a mean value of 39 IU/l (International Units per liter), standard deviation = 3.4 IU/l. Calculate the 95% confidence interval for the population’s true mean value of plasma alkaline phosphatase. Show your...
  20. E

    Mean Significance Statistical Test

    3. In two wards for elderly women in a nursing home the following levels of hemoglobin were found: Ward A: 12.2, 11.1, 14.0, 11.3, 10.8, 12.5, 12.2, 11.9, 13.6, 12.7, 13.4, 13.7 grams/dl Ward B: 11.9, 10.7, 12.3, 13.9, 11.1, 11.2, 13.3, 11.4, 12.0, 11.1 g/dl Ward A Ward B n = 12 n =...