sample size

  1. F

    calculating sample size needed by future studies having got my Logistic Regression

    Help anyone? I have downloaded Gpower 3, and seemingly found the option: under test family: z tests statistical test: logistic regression type of power analysis: a priory compute required sample size (given alpha, power and effect size). then I am not so sure whether I have one or 2...
  2. T

    Need Help in STAT Project

    Please help me I have this project for Stat in Excel. I need to answer the following questions in the the attached worksheet. I have completed questions 1 - 4, But I am having hard time figuring out question 5 - 9. Please help me I am desperate. thank you. The College Gift Shop wants to have...
  3. G

    Standard deviation - how many samples to I need to measure to get a "good" one?

    I was looking at Minitab 16's Power and Sample Size calculation tool for a one sample t-test. If you're not familiar with it, you can put in 2 of the 3 factors: sample size, differences, and power values. You also have to put in the standard deviation. This got me thinking. How do you know...
  4. S

    How can i calculate the sample size in this situation?

    I am designing a RCT between two interventions (two closure techniques of abdomen after an operation) to assess their safety, the safe intervention will have the less percentage of outcome (dehiscence). The problem is that i know the outcome of one intervention (p1): 0.2 % while for the other...
  5. C

    Minimum sample size

    Hi Everyone, I have spent hours on this and cannot seem to get to the answer. Here is the questions: Calculate the minimum number of children that will be needed in the study to allow paired and unpaired analysis to be performed based on the the following assumptions. First, it is...
  6. L

    Needing a bit of help with sample sizes :)

    Hello, I'm new here so apologies if this is a simple question, I have tried a search online and here, but I'm am rather stuck. I am trying to do a sample size calculation for a multiple pairwise comparison. Within my study, participants are given three types of candy (A, B, and C)...
  7. C

    Number of samples / sub-samples required for students t-test

    I have a batch of material (25kg limestone) which contains low concentrations of several elements. 100 g samples are taken from this batch and undergo a process which may lead to the concentrations of these elements to increase or decrease (though more likely to increase). Following the...
  8. L

    Minimum sample size for moderation analysis

    Hi everyone, And thanks for the great job you are doing here. I have a question regarding statistical power and regression. How can I calculate the minimum sample size based on the number of moderators I have in multiple regression? Is there an online tool for this? If for example I have 5...
  9. A

    Advice on sample frame and sample size

    I'm involved in a 4-yearwater supply, sanitation & hygiene project for mainly pastoralist (nomadic)communities in northern Kenya. We need to conduct a baseline survey for anumber of indicators against which the project will be later measured. As anon-statistician I'm struggling with applying...
  10. U

    Sample Size Difference in Kruskal Wallis- big problem or little problem?

    I know Kruskal Wallis can handle "some" difference in sample size. but is comparing 3 set of data with the sample sizes n=170, n=139, n=44 going to throw things off too much? Thanks
  11. T

    Calculating Sample Size for a prospective/longitudinal study

    I am an undergraduate conducting a literature review. I am wanting to discuss sample size among the papers I am critiquing. The papers I am analyzing are studying hearing impaired populations over a given time, to discover whether they are more susceptible to cognitive decline. How do I...
  12. G

    Sample Size calculations with sub-groups

    I am in a situation wher we need to recruit 1600 people with a particular condition (calculated so that we can detect a 5% change following intervention). We also want to test the intervention on a particular sub-type (drug-users), where we expect a higher prevalence of the condition, and want...
  13. R

    Fractional Factorial Design Question

    Does anyone have experience with using fractional factorial designs for psychological research? I'm new to DoE, and I have no guidance except the internet... not too helpful. Anyhow, I have a practical question about data collection and entry (e.g. minitab) The question is: if I have...
  14. F

    random-effects regression in STATA

    I am looking at whether group differences (parkinson's patients versus age-matched healthy controls) exist in the performance of a perceptual task that has two DVs: reaction time and error rate and two stimulus exposure durations (preconscious and conscious). I have run the main analysis which...
  15. L

    proc power onewayanova

    Nevermind, I was not getting any responses :(
  16. L

    When to assume Normality

    I am working with a rather large sample (approximately 120). Typically, I would not have any issues justifying normality due to the large sample size and that the Central Limit Theorem would allow me to make that justification. However, of the 120 or so samples, there are about 8 extreme...
  17. S

    chi square test

    I am running a chi square test, followed by a marascuilo test to compare a binary resonse with categorical variables as the independent variables. The dilema is that my total sample size is 1,000,000 so I am getting chi square values in the thousands, with no major differences in the actual...
  18. R

    Help with power analysis!

    So, I've never taken a statistics course before. Just completed my honors thesis and graduated. Now I'm trying to do power analysis (post hoc) on my data. Using G power, please help me with what to do/how to interpret the results. First of all, I looked at two independent groups (group 1...
  19. S

    extremely small sample size

    I have a Y variable that is measured in parts per million (ppm). However, it can be converted to a binomial variable comparing against a p=.1. The problem is only 4 samples were collected, and the response of telling them to collect more samples is not possible. Is there any statistical test...
  20. D

    Required Sample Size Calculation

    First time forum user and STATS novice so I apologize on many fronts. I'm working on a customer survey to help forecast future product sales. We have current customer data for 2009 and 2010. From that we are trying to determine what sample size (number of surveys) we need to be able to...