confidence interval

  1. 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...
  2. 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...
  3. 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?
  4. 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...
  5. 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 =...
  6. 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...
  7. 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...
  8. 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 =...
  9. 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 =...
  10. 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...
  11. 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...
  12. 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...
  13. 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...
  14. 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...
  15. 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...
  16. P

    Confidence limits of chance

    I am looking to determine the confidence interval of chance for a three class problem. I know i need to use binomial test, but am not sure that all my values are correct. Number of samples per class = 60 per class. I want the value for alpha = 0.05 (so the 95% CI) I believe it would be from...
  17. S

    Weighted confidence interval for mean?

    Lets say we have values v = (0,1,2,4,8,10) with weights (real numbers not necessarily integers) w = (0,10,1,1,1,1) Calculating the weighted mean is obvious: m = sum( w_i * v_i) / sum (w_i), but how do I get weighted confidence interval (lets say with 95% confidence)? The standard...
  18. N

    No mean and standard deviation for confidence interval.

    According to the government, 23% of all American adults have more than one job. A random survey of 68 adults finds that 21 of them hold more than one job. At the 5% level of significance, can we accept the government's claim? For this problem the solution would be like this Ho: P = 0.23 Ha...
  19. G

    Significant p-value, but 95%CI includes 0

    Hello everyone, I have the following problem: The result of a Pearson correlation (sample size = 177) was significant, r = .127, p = .048 (one-tailed). However, the 95% confidence interval includes zero, 95% CI [-.02, .27]. How is it possible to have a significant p, when the CI...
  20. M

    Confidence intervals for multiple proportions

    Hi everyone, I would like to know how to calculate confidence intervals for non-binomial proportion data of which I have multiple samples? I'll give an example to clarify: Proportion1 Proportion2 Proportion3 Proportion4 Proportion5 Proportion6 Sample1 0.93926 0 0.00204 0.0585 0.0002 0...