sample size determination

  1. M

    Group Size for Binary Logistic Regression

    I am trying to determine the odds ratio for the effect of C on A. However, my is a sample of n = 45 with 4 = yes and 41 = no. Is this small group size a major issue, and how do test for power in this case? THANKS!
  2. B

    Estimating sample size for reliability study

    Hello, I'm having problems calculating the required sample size for my PhD study. I have designed my first study, which is comparing moral reasoning abilities in people with a brain injury to a healthy comparison group. I have used previous similar research and G Power to estimate the...
  3. 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...
  4. L

    Please help - Sample size calculation

    I am designing a study in which a new drug x is given to patients on drug y and then drug y is withdrawn. If the required success rate is 80%: How should I calculate a sample size with a power of 90%? Thanks for your help.
  5. P

    Sample size - chi-squared vs. normal

    Hi, I apologise if this is the wrong thread. I need to calculate sample sizes, but I'm curious as to why the commonly used Krejcie-Morgan tables use a chi-squared formula rather than a student-t or a normal distribution. I see quite a few other papers that use the latter distributions...
  6. Y

    help with study sample size and statistical analysis

    Hi, I'm in the preparation stages of an RCT looking to assert the effectiveness of psychological therapies for a health condition. The design will be a 3 parallel arm RCT, comparing high intensity CBT, low intensity CBT and usual care. We are thinking of collecting baseline measures (2...
  7. B

    Unblinding Concern: Projecting Last Event in > 2 Arm Study....

    In a two arm time to event study one can use various blinded projection methods using the aggregate event rate to estimate when the last event may occur. Now, lets say one has a three arm study where two different doses of an experimental drug are compared to a control. In addition each...
  8. R

    sample size determination using a population range

    Hi. I have a problem about sample size determination. The population of interest is somewhat vague. What I know about the population is only the population range R, i.e, R = max value - min value in the population. I don't know the population distribution, also. Is it possible to...