sample size

  1. J

    Sample size determination for ANOVA / KRUSKAL WALIS

    Hi! I need help with my dissertation regarding sample size calculation. I will be grateful if anybody can help me out with this... My study involves two aspects... 1. Comparison of a quantitative variable - between cases and controls 2. The cases are further classified into four...
  2. C

    Sample Size Calculator (one group versus population)

    Dear all, so far I couldn´t find a solution to calculate the required sample size for the following scenario: Goal: Research continuous variables (cost perceptions) of a population through one sample group. --> means of one group need to be significant for the entire population...
  3. D

    Sample Size Calculation/power calcuation for retrospective study

    Hi all, I recently completed a study looking at hospital records over a 5 year period (fixed population of participants based on study period). We looked at 'blood transfusion' as a binary measure (didn't receive a transfusion = 0, did receive a transfusion = 1) between three groups...
  4. K

    Sample size estimation for multinomial autocorrelated data

    I'm trying to work out the minimum sample size needed to accurately characterise land cover data. The idea is to set out the a number of quadrats across the study site and identify what land cover type occurs in each. I have an idea as to how many categories there should be. So this is a...
  5. E

    Help for sample size calculation

    in my prospective cohort study I will assess the serum level of a vitamin in a group of patients the normal reference serum range is 10-30 in normal population there is no control group then i will correlate the serum level with later occurrence of outcome (yes or no) So I need to...
  6. J

    Calculate sample size?

    You are interested in studying the relationship between sodium consumption and the development of hypertension. 32% of Americans are hypertensive (systolic blood pressure>140), and a further 29% are prehypertensive (140≥SBP>120). Detecting a 1 mm Hg SBP elevation with 80% power at the 0.05%...
  7. M

    Help with statistical power?

    Hi, I'm doing a study looking at the ability of a test to detect a change in bacterial numbers pre- versus post-treatment [i.e. not treatment effect, but pilot study looking at efficacy of the test used]. I've done a chi-square test and got a significant result (p<0.05). However given that I...
  8. R

    power calculation for two groups (parallel)

    Hi I have got 400 and 600 samples in control and test groups respectively. And in each of these two groups, i have an effect variable that occurs at the rate of 30%. this is a retrospective data analysis. I want to investigate whether the effect variable impairs the patient outcome (response...
  9. M

    Census data: Should I worry about sample size and pvalues?

    Hi all, I have a questions regarding statistical power and sample size. (1) Do I have to worry about sample size in a multiple logistic regression if I am using all the individuals in a population (census) and not a sample? Let’s say that I want to see how many tourists in a resort report a...
  10. A

    Need help with power analysis GPower Novice

    Hello everyone. I am doing a power test for Fishers Exact Test on GPower, and dont know how to determine the proportions p1 and p2. I have 2 categories that im looking at if there is a difference between one and other across 4 rows. How would i calculate the P1 and P2 for this. Basically i...
  11. B

    Please help: ANOVA

    I'm asking a group of young people who have experienced loss to complete the Posttraumatic Growth Inventory and then a sheet about different factors identified in previous research (age, gender, support network, religious beliefs, etc). I then want to see if there are any correlations between...
  12. W

    Clinical Trial - sample size for statistically comparable data?

    Hi Everyone In a nutshell - I am looking to undertake an 8 week clinical trial of an equine veterinary health product. I am wanting to analyse corticosteroid concentrations deposited in the keratin of mane hair at Day 1 and then Day 56. I was hoping that 20 horses would be a sufficient...
  13. W

    Clinical Trial - sample size for statistically comparable data?

    Hi Everyone In a nutshell - I am looking to undertake an 8 week clinical trial of an equine veterinary health product. I am wanting to analyse corticosteroid concentrations deposited in the keratin of mane hair at Day 1 and then Day 56. I was hoping that 20 horses would be a sufficient...
  14. K

    Relationship between effect size, sample size and p-value?

    Is there a simple formula that links effect size, sample size and p-value? Specifically, how does the p-value depend on effect size and sample size? Are there any other critical factors involved in this relationship? I'm basically looking to understand how these factors are linked...
  15. L

    Power and sample size calculation for neuroscience

    Dear TalkStats, I have searched the forum but cannot find the answer I am looking for, if you could help that would be great! I am recording cells and their action potential frequency in two conditions (group 1 and group 2). (So it is a repeated measures.) How do I calculate the required...
  16. T

    please help me justify sample size for a pilot clinical trial

    I'm a bit desperate for statistical help so trying out all avenues. Any guidance appreciated! I need to justify a sample size of 30 or 32 (15 or 16 per arm) for a placebo-controlled pilot clinical trial of a drug. This is all I can afford, but that is not a good enough justification for...
  17. T

    how to justify a sample size for an underpowered pilot study

    moved to biostatics: how to justify a sample size for an underpowered pilot study UPDATE: I reposted this in the biostatistics forum. I also added some more details, mainly my not-fully-formed thoughts about how to proceed. Thanks! I need to justify a sample size of 30 or 32 (15 or 16 per...
  18. B

    Power analysis and sample size

    Hello all, I've used perused this site numerous times in the past for assistance with statistical issues, but this is my first post. I work with fish, and am specifically interested in the environmental effects on these fish. I ran regressions of growth increment (growth experienced in a...
  19. K

    Sample size calculation for cross-sectional survey (2 Time points)

    I am working on a study design for a study to determine behaviors and structural barriers to health seeking at baseline for HIV negative young women 15-19 years, conduct interventions for 2 years and later study their behavioral changes and remaining structural barriers after intervention. This...
  20. R

    Calculation of Sample Size for one-way ANOVA

    Hello, I have problem of calculating sample size for one-way ANOVA. My settings is the following: Population size = 100 Controlled group = 1 group Treatment group = 2 groups Power = 0.8 Alpha = 0.05 Group allocation ratio: All groups have the same sample size standard deviation of...