sample size

  1. R

    Large Sample Surveys

    Dear Forum, I encountered an employee satisfaction survey report which sampled 50,000 employees (try not to laugh, that's a sample not the population). The authors reported % agreement based on Likert scales, which is not great, but ok, and compared said "scores" to a normative benchmark (for...
  2. J

    Wellbeing Survey - Sample Size to identify minimum 2% effect size

    Hi I am currently trying to determine a suitable sample size to detect AT LEAST a 2% increase in high levels of life satisfaction. The survey is on wellbeing and is made up of 10 scale questions (0-10) and 1 open-ended question. The current sample size I have determined is around 8571 (80%...
  3. K

    Don't know how to statistically justify sample size

    I'm a newby to the forum, thanks in advance for your help. I'm planning to test some parts but because of all the replicates I can only afford to test 6 parts. The success criteria is after accelerated aging and chemical treatment the destructive pull force of the materials must not be less...
  4. E

    Event study - varying sample size per event window allowed?

    Hi all, I am conducting an event study, analyzing how social media posts are affecting stock prices. Is it statistically allowed to have a different number of observations per event window? E.g. to have in event window [0;1] 120 observations for which the abnormal returns are analyzed...
  5. M

    RCT: estimation of total sample size knowing only the percentage of occurrence

    Dear all, I was asked to estimate the minimum sample size to set up a RCT comparing a standard dose technique to detect recurrence of disease vs low-dose technique. It seemed to be reasonably to me to think about differences in sensitivity and to suggest a noninferiority trial comparing the...
  6. S

    Equal or Unequal Samples when comparing more than two means? Does that matter?

    I am going to conduct a study in which I'm going to analyse the mathematical performance of indigenous students in school A and will be compared to non-indigenous students in public-urban (school B), private-urban (school C), public-rural (school D) and private-rural (school E) schools to...
  7. B

    Central Limit Theorem Indicative of Underlying Distribution?

    Hi All, I've been reading threads off and on for a couple days, and I can't get a good feel for how to answer this question I've got stuck in my head. I'm sure the answer is in here, but I'm an engineer, not a statistician, so I can't make the leap to apply the posts I've read to the...
  8. S

    meta-analysis vs. random effect combined analysis

    I have data from 200 similar studies, all measuring the same effect of a continuous independent variable on the same continuous response. I say similar because the designs are different (split plot vs. rcbd) and the levels of the independent variable is not the same across all studies. I have...
  9. S

    Determining sample size from confidence interval and significance level

    Hi everyone, I am studying a university level stats course at the moment and I have been given some excerises to take home that I am struggling with. I am asked to calculate sample size for a hypothesis that requires an 90% probability of detecting a difference at a significance threshold of...
  10. M

    Survey uncertainty with a given population proportion

    Hello! I have to estimate the uncertainty of the result of a survey where there sample size was defined to have an uncertainty of 2.76%, based on p a p value of 0.5. The 2.76% error is calculated assuming a 50% population proportion, which is a worst case scenario assumption: size...
  11. I

    regression analysis for very small sample?

    hello, my study is about "The impact of corporate governance on firm performance". my sample size is 5 compagnies i have 6 IV and 1 DV so my Q is, could i use regerssion analysis with such small sample size? if no, what is the best alternative to choose? thanks in advance
  12. 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...
  13. 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...
  14. 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...
  15. 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...
  16. 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...
  17. 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%...
  18. 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...
  19. 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...
  20. 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...