# Tagged Questions

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### How to test for normality of growth disturbances in chemo treatment?

I'm a med student, conducting a retrospective analysis of weight/growth disturbances during chemo treatment. I wonder, if I should: assume, that growth is a variable normally distributed across the ...
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### Standard errors of regression coefficients based on sample size

For any particular nonlinear regression: $$Y_i = f(\mathbb{x_i},\theta) + \epsilon_i, i=1,...,n$$ I currently have standard errors for each of the $\theta_j$ obtained via the Gauss-Newton algorithm ...
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### How to add confidence intervals to describe the variability in monthly samples of data?

The data analyzed here is a sample of individuals collected on a monthly basis. What would be the best way to compute confidence intervals for the monthly sample means, in order to indicate the ...
98 views

### Comparing patient and control group results of a survey

I have data from a survey given to a patient group and control group. Both groups completed the same exact survey (Likert scale). One group has an n of only 5 or 6, the other n was about 15. What ...
38 views

### Determine sample size without knowing standard deviation

I want to calculate the required sample size for a call centre with a finite population. The survey will collect data on many variables. The objective is to gain data about a range of psychological ...
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### How to standardise cases within groups to perform ranking across groups and over time?

I am trying to create a method to rank ships according to their fuel burn rates. There are two different classes of ships, with different burn rates, so I am trying to create a mean and standard ...
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### Rules of thumb for minimum sample size for multiple regression

Within the context of a research proposal in the social sciences, I was asked the following question: I have always gone by 100 + m (where m is the number of predictors) when determining ...
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### Does the intercept count as a parameter for the n/parameters sample size rule for multiple regression?

When estimating parameters, I know the general rule of thumb is n/parameters should be >10. Does the intercept in a model count as one of the estimated parameters in this "rule"? For example, if I ...
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### Compute the variance of parameter estimates given limited number of samples

I'd like to infer the variance of estimated parameter $\hat\theta$ of the density function of $f(x;\theta)$ given only a limited number of samples $X_1,\cdots,X_n$. Bootstrapping doesn't perform well ...
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### How to determine the sample size of a Latin Hypercube sampling?

I am designing an experiment with 5 variables. Some of the variables have 2 and others have 3 levels. The method that I am going to use is the Latin Hypercube, but I do not not what the sample size ...
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### Types of regression that might work on small samples

I know that this kind of discussion might be both a silly...very silly and a hot issue simultaneously...but I thought it would be nice to raise it : Which types of linear AND non-linear regression ...
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### Question regarding sampling, estimation and accuracy [closed]

Let's say there are N chunks of metal, each are 4 inches thick. They are to be hammered and reduced to following best possible sizes: 1, 2, 3 or 4 inches. If we were to use sampling to get an estimate ...
181 views

### How does confidence interval vary with sample size?

I am trying to convert state-level poll results for 2012 U.S. presidential election into state-level probabilities of each candidate winning. To achieve that, I am using the logistic function, which ...
244 views

### Predicting dependent variables where independent variables are samples with differing sample size

Is there a standard method of dealing with independent variables, where they are samples from a known distribution, and the sample sizes differ from sample to sample? I'll give an example of what I ...
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### How to back-calculate change from baseline from a p-value for a paired t test

I have a result from a study in a research paper which gives a mean/SD for 2 time points (pre & post treatment), and a p-value based on a paired-samples t-test. What I want to calculate is the SD ...
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### Interpretation of Spearman correlation for small sample

I am currently being confused by different opinions regarding the spearman correlation interpretation. Some says, $\rho<0.2$ can be ignored as small/weak relationship, some says $\rho<0.1$, for ...
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### Visualise data with different sample sizes

I did a literature review and ended up with a lot of data in the kind of "10 out of 20 studies found x while 4 out of 8 studies found y". To be more precise; I looked up the contribution of seafood ...
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### Normality assumption and sample size

I know this is a very debated topic, even on this site, but I still couldn't find an answer to my problem. Recently I am working with large samples (300, 400 and more). For now, I am trying to use ...
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### Comparing the result of a study which has unequal group sizes

I have conducted two user studies and in my studies I didn't have control over the group sizes. In each study users were put in groups and they were asked to perform some group activities. Here is the ...
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### Precision, Recall and area under ROC curve as sample size increases

The following is a question from an exam paper on evaluating the performance of search engines. To this day I looked in my text book and literally close to 50 web pages and I can't find one convincing ...
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### How to justify the sample size? [closed]

I'm wondering how can I justify my sample size! I have 45 observations and 6 independent variables from which one is control variable. Is there any rule of thumb or specific test in this regard? Many ...
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### Repeated 100x 10-fold cross validation, what is the sample size when doing an significance test?

I iterated my 10-fold cross validation 100 times for several methods. Now I want to use a t-test to test if the results are significant. However, I'm not sure what the sample size is. Is the sample ...
353 views

### Power calculations, logistic regression with continuous exposure--cohort

I'm trying to estimate power in a logistic regression with a continuous exposure in a cohort study (ie, the ratio of the sampling probabilities is 1). I have population cumulative incidence ...
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### Given a small pilot study, how to compute number of samples needed for a certain power?

I ran a small pilot study and computed both a p-value and Cohen's d. Now how do I compute the number of samples needed for the full study if I want a given power (e.g. 95%). I hoped I could use this ...
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### How to calculate sample size needed for comparing the “change from baseline” scores between two groups?

I'd like to know how to calculate the sample size needed for comparing the "change from baseline" scores between two groups? Thank you in advance for your consideration
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### For bootstrapping, why does a higher subsample size lead to lower variance?

I've been working on a bootstrapping problem that's left me a little confused and wondering whether I'm doing things correctly. We have around 200 samples from a population of about 3,400, we want to ...
1k views

### Is the number 20 magic?

I have references that advised to consider a sample size of minimum 20 for data fitting distribution. Is there any sense in this? thanks
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### Sample size and hypothesis testing problem in linear mixed effect models

I have a dataset about the growth of an aquatic plant in different sites (lakes) and months. In particular I have 3 sites and for each site 3 plots in which the biomass of 3 plants was measured. The ...
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### G*Power-Repeated measures MANOVA “number of measurements” input field

I am trying to calculate the sample size needed with G*Power for my dissertation study. I will be doing a Repeated Measures MANOVA within/between interaction. My question is in the field "number of ...
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### Sample size calculation for multivariate problems

I am interested in multivariate investigations. I have been trying to learn about designing such experiments where there is one dependent variable (a class/group) and many independent variables that ...
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### Sample size determination crossover study

I would like to have some help with this sample size determination. This is a 2 ways, 2 period crossover study to evaluate a drug drug interaction Design: TR RT Parameter to evaluate AUC ...
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### How does the confidence interval for the parameter p of a bernoulli trial vary with the value of p itself?

This is a very basic question (I'm currently studying undergrad level statistics), but I was hoping for some clarification regarding an assertion I read in a newspaper article earlier today. The ...
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### How to find Coefficient of Variation with E(X), E(X^2) and sample size?

Given E(X), E(X^2) and sample size. How do I find Coefficient of Variation? Variance = E(X^2) - E(X)^2 sd = square root of variance Coefficient of Variation = sd / E(X) however, with the values ...
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To help me focus on which pages on a site to improve, I'm looking at user feedback to the question "Was this page helpful?" (Answers are "Yes" or "No".) The response rate (responses divided by unique ...
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### Optimal sample size for panel data

Is there a way to calculate the optimal sample size for a balanced panel over 8 years from a population of approximately 30,000 and involving 10 variables being studied, say for 95% degree of ...