1. M

    When do sample size calculations need to adjust for clustering?

    I am aware that sample size calculations for cluster RCTs must adjust for clustered data. I would like to understand better if such adjustment might be necessary for other study designs. For instance, I am working on a nested case-control study to identify clinical and socio-demographic factors...
  2. Y

    [JMP] Does any body can explain me on one sample size what formula used in JMP?

    Hi, sir. As below table, I have so many items to do analysis with One, Two, K sample mean. Is there any jmp formula in "Sample size N" same as jmp under DOE "Sample size and power" Please help me. Item Sigma σ Delta δ Sample size N Method A 1.0088...
  3. T


    So I'm starting a website (see thread title) devoted to statistical power analysis and sample size determination. Why? B/c I make power/sample size calculations all the time in my work. Sometimes a common statistical test will do; sometimes something a little more complex. But, invariably...
  4. V

    What to do if sample size is too big? (ttest)

    So I'm running ttests for a descriptive statistic table and all my results are significant, but I"m concerned that the sample size is too big 3,880 obs for each of the two groups. (This is bank data by qtr appended into one file.) I understand that the large sample size is probably making...
  5. 1

    Sample size for ordinal logistic regression (or at least ordinal)

    Sample size for ordinal logistic regression (or at least logistic regression) I am trying to determine the sample size I need for my dissertation and I have no clue where to begin. I have been unable to find a sample size calculator for ordinal logistic regression and was told by my chair to...
  6. Z

    Question about sample size and margin of error

    I am trying to determine if my dataset sample size is large enough to be statistically significant. I'm using a 95% confidence interval. However, every formula I've found uses margin of error---and to calculate margin of error, I need a sample size. This seems circular, and I am lost.
  7. S

    Sample size calculation

    Hi all, if got the a question concerning sample size calculation: When doing a sample size calculation for a randomized clinical trial for comparing to group means I know the following formula: n= \frac{r+1}{r} \frac{\sigma^2 (Z_{\beta}+Z_{\alpha/2})^2}{difference^2} Now my question...
  8. N

    Need help determining sample size

    Hi, I've been asked to analyze a tool that gives out quotes to our customers. There was feedback that some of the quotes are wrong and the team wants to know how often this happens. I found a sample size calculator online,http://www.surveysystem.com/sscalc.htm, but I am having problems...
  9. A

    Post-hoc Power, effect size for Chi-square

    I need help with my post-hoc power analysis, specifically the effect size: I measure children's successrate under four conditions. My dependent variable is nominal (specifically binary, with the values 0 (failed) and 1(succeeded)) My independent variable is nominal with four categories. My...
  10. N

    Power of a one sample t-test

    Hi all, I have a little problem with power calculations. I have calculated the power for a one sample Z test, which was fine. I found the critical value under H0: X_{a}=M_{0} plus+ Z_{\alpha }\cdot \frac{\sigma }{\sqrt{n}} then I calculated the Z value under a specific value for H1, and...
  11. S

    Determining the power of a 2-Sample T-Test

    So I am running a two-sample t-test , and wanted to set some preliminary accuracy goals. Ideally, I wanted to end the test when there was a statistically significant difference, using an alpha level of 1%, and power of 90%. However, this will be my first time setting a power criteria for...
  12. N

    Power of t-test

    Hello all, I want to write an R procedure that calculates the power of a simple two samples t-test. Does anyone here has an idea how to do it ? Thank you !
  13. I

    setting parameters in G*power for correlation tests

    Hello, everyone :) Need your help on how to set parameters in G*power... I am doing two very simple tests: one on pearson correlation between midterm scores and quiz another one on partial correlation between the same scores with motivation score as controlling variable. I need to run a...
  14. A

    Statistics Final Exam Question

    Due to some gray area in a TA's grading, I am going to review my statistics final with my professor on Friday. There's some possibility of a grade change. One of the questions I'm most anxious about, the final question, went essentially like this: "Tommy finds a deck of cards, but he is not...
  15. J

    How do you calculate n^m for large n and m?

    Hi! I'm quite new to R (and this forum..), today I tried to calculate n^m for some large n and m. The results were too large. For example, 20^300=inf. How do you calculate it? Is there a function for approximation of n^m of large n or m? Thank you:D
  16. G

    Help needed for a difficult scenario!

    I would appreciate help to understand how to appropriately analyze the following data. I have 3 groups: n1= 105, n2= 105, n3=15 (yes, just 15) Groups n1 and n2 are related (i.e siblings), thus not independent of each other as the data are under genetic influence; group n3 is not related to...
  17. R

    Power calculation in Critiquing Tool

    Hi all I am currently trying to critique some orthopaedic research papers using the Downs and Black (1998) critiquing tool, but I am completely confused by the final question. It asks: “Did the study have sufficient power to detect a clinically important effect where the probability value for...
  18. C

    Power of Significance Question

    Given n=24, significance level=.05, and standard deviation=10, what is the the power of the significance test? The book says its .80 and that makes the beta = 1-.80= .2. But I do not see how they got this. Please thoroughly explain how they got .80 as the power. Thank you.
  19. T

    Power curve of distribution with 2 parameters

    Hello. I want to obtain a power curve for goodness of fit test of a distribution with 2 parameters, let say A & B. My test is actually about parameter B. And say mean=A*B. So, I'm curious of how should i generated the sample to get the power? Should i generate samples with all the same mean...
  20. M

    Power calculation in regression for curviliear effect

    Hi! I performed a regresson analysis to test a curvilinear effect. I've followed Aiken & West procedures Center X, Squared centered X Enter X 1st step Enter X2 2nd step However, in the interpretation of the results I would like to test the power of this regression, considering the...