# sample size

1. ### Why does bootstraping with 50% samplesize and no replacements always gives appropriate confidence intervals.

Hello, I compared different ways to calculate confidence intervals. On the one side I used the direct formular on the other side I used a percentile bootstrap methoden. (Calculate the statistic (e. g. mean) on n subsamples and choose the a/2 and 1-a/2 percentile for the confidence interval.) I...
2. ### Simple Sample Size Calcs

Hi all, I am looking into the feasibility of mailing (post) churned customers with various long regencies. I want to get an idea of their likely response rates by recency with a small test prior to rolling out to some or all of these regency’s. Using online calculators or the formula behind...
3. ### Can you use finite population corrector in getting the sample size of an analytic study?

Our research is about burnout and its associated factors. In computing for the sample size, we used open epi calculator, the one for cross-sectional study design. (We computed for each factor we wanted to associate and looked for the highest sample size.) We obtained a very big sample size...
4. ### Question: Single person - T-test?

Can you look at improvement in scores across two time periods, if you have hundred of data points but they are all from a single individual. Can I do a t-test to compare the indvidual's scores over one period to the same individual's scores over a later period? I've never encountered anything...
5. ### Checking the adequacy of the sample size when the data set is qualitative

I am trying the check whether my simple size is adequate. I have activity patterns for a set of people (An activity pattern is something like (1,2,9,3,4)). These activity patterns are qualitative data and due to that reason I cannot calculate a Standard Deviation using below equaltion...
6. ### How do I determine the minimum number of observations needed per category in categorical predictor variables?

When conducting a simple linear regression analysis with one categorical predictor variable and power projected at .80, G*Power suggests a minimum sample size of n = 55. Now, assume that the predictor has three categories, and that I obtain 55 necessary responses. What does it mean for the...
7. ### Applying One Tail Test to Daily Data to Estimate Monthly Values

This is my first post in this forum so I apologize that if I am not formatting my question as seasoned forum users. I have sample of daily historical usage data for part numbers at a factory. There are hundreds of part numbers in my data set. I want to use the historical usage to calculate...
8. ### Mechanical Engineering Sample Test Size

You need to conduct an engineering 3-Point Bending. How many samples should you test? I was recently asked this in an interview but was not sure how to answer. I tried saying that it would depend on time, the readiness of the samples, and the cost of the tests but the interviewer said to...
9. ### Minimum Sample size for multiple linear regression

Hi, I tried to calculate the minimum sample size for multiple linear regression. I tried to check the sample size for predictors=4, effect size f=0.2/d=0.2, sig.level =0.05, power=0.8 1. When I checked the power of the entire model (F power) n=304 2. When I checked the power of one...
10. ### CLT - What sample size is large enough? your thoughts?

Hi, I will glad to read your thoughts Whats sample size is large enough so I can assume normality based on the Central Limit Theorem? Some write 30 some write 100. I run some simulations and it seems that for some skewed data (finite variance, independent ...) you need a sample bigger than...
11. ### How to calculate sample size to check if 95% of values are between predefined upper and lower limit

Dear Forum, I am stuck on a sample size estimation question. I looked at the FAQs and the previous questions but I do not think the answers there apply to my scenario (correct me if I am mistaken). Imagine I want to produce apple pies. My pie only tastes good if the apples have an acid content...
12. ### Guidelines for building a statistical model for a business problem?

Hi There, I would need some guidelines for creating a statistical, probabilistic model for a business problem I'm dealing with. Here is the problem: I have a website that connects tourists to tour guides. When a new inquiry comes, a tour guide is assigned (today quasi randomly) to the...
13. ### sample size for dichotomous outcome in retrospective observational study

I really need some help here seeing if I can get this right. I seem to come up with something different every time. I am testing the hypothesis that there is no difference in the timing of removing chest tubes to the development of significant pleural effusions after surgery requiring drainage...
14. ### power analysis/ sample size

Dear reader, I would like to conduct a clinical study in which I compare 2 treatments. The goal is to determine which one cures the lesion faster. There are currently no studies comparing these two treatments head to head but there are studies comparing them to placebo. According to the...
15. ### Regression analysis sample size

Hello, I am undertaking a study looking at patients with AF (a heart rhythm disorder). I'm looking at how continuous baseline variable (X) predicts a improvement (a continuous measure of function) (Y) after a discrete treatment. I plan on using regressional analysis after collecting the before...
16. ### GPower f (V) effect size interpretation

I am having difficulty understanding how to interpret effect size f(V) on GPower for a priori sample size calculation for ANOVA repeated-measures, within-between interaction. I am conducting an a priori power analysis to calculate sample size for ANOVA repeated measures, within-between...
17. ### 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...
18. ### 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%...
19. ### 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...
20. ### 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...