sample size

Hello there, i'm a clinical researcher currently involved in setting up a study to determine whether a certain profylactic treatment to reduce post-operative complications is effective. However, i keep running into all kinds of different sample size calculations and different effect size...

Hello! I am a bit stumped with the research I am conducting and wanted to ask for some advice/insight. My study involved having 4 individuals complete the same 3 measures at pre- and post-test. So each individual completed each measure before receiving an intervention, and then completed the...

Hello, I have some data that I want to analyse. It is 2x2 within-subjects design. My DV is continuous and the two factors have 2 categorical levels. But I only have 8 subjects, so I am unsure about how to proceed. Is it correct that there is no reasonable alternative to just using an ANOVA? If...

I have the following situation: 6,000 letters created in July 250 staff created the letters Some staff created more letters than others I'm looking to do a quality assurance exercise where we check the quality of a sample of the letters created by the staff. I need some help to understand...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...