confidence interval

  1. 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...
  2. 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...
  3. 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...
  4. 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...
  5. 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...
  6. 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...
  7. 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...
  8. 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?
  9. 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...
  10. 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 =...
  11. 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...
  12. 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...
  13. 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 =...
  14. M

    sample size calcs - why do these produce different results

    What are the interpretations for each of these? data a; input z p q e; cards; 1.96 0.95 0.05 0.05 ; data b; set a; n=(z*z*p*q)/(e*e); run; proc print; run; ****************************; proc power; onesamplefreq test=z method=normal sides =...
  15. C

    Graphing My Confidence Interval Data

    Thanks for looking at this. I might be approaching this problem the wrong way because it seems like it would be simple to graph three lines for which I have data. I have plotted a line that represents a mean species diversity estimate (Y axis is species count, X axis is individuals...
  16. S

    Net Promoter Score - Calculating Confidence Intervals and Margin of Error

    Hello, In my sample of 1162, I have 291 Promoters, 476 Neutral and 395 Detractors. I therefore have an NPS of -9. We have calculated a confidence interval of 4.4. Question : Should this be reported as -9 +/-4.4, or is the confidence interval the entire range, in which case it should be...
  17. J

    confidence interval that violates physical boundaries

    :wave::wave::wave: Hi, Colleagues, A model is supposed to predict a value that represents proportion, namely, the predicted value should be in [0,1]. However, model is just a linear regression, producing confidence intervals violating the boundaries of [0,1]. Of course it is not an adequate...
  18. X

    Urgent: Hypothesis Testing with unknown standard deviation

    Hi, I'm having a lot of trouble figuring out this problem without knowing the standard deviation. Please if anyone could help me that would be very much appreciated. Thank you! I also don't know how to calculate anything other than a 95% confidence interval. A national survey conducted in...
  19. F

    finding Confidence interval without CLT

    Hi all, I searched the posts and I did not get what I wanted. so here is the question: In our Hw we are given daily sales of pastries and coffee for a shop in a semester(which is 70 days). it means I have a mean and a standard deviation for each. Knowing that coffee or pastries are 3$ each...
  20. C

    deriving the upper confidence interval limit in robust linear regression using MASS

    Since my data to some extent violates the linear regression assumptions I decided to also test the model using robust estimation limiting the influence of outliers. However, I find it difficult obtaining the standard deviation of the estimate. I use R with the package MASS and the command rlm...