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...

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...

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%...

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...

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...

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...

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...

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...