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# Questions tagged [sample]

a sequence of objects or individuals collected from a larger (possibly infinite) population or process.

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### Power analysis for the Cox proportional hazards model

I'm trying to work out the sample size needed for an RCT based on a small study looking at reoperation following index surgery. In this small study, there were 1000 patients, group 1 had 700 versus ...
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1 vote
0 answers
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### cloglog.sample.size function (Binomial distribution)

I was wondering if cloglog.sample.size function from binom package in R can be used to calculate the sample size for the following model (Binomial dis with cloglog) which can be used for discrete ...
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1 vote
1 answer
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### Standard deviation on result of calculation

I'm calculating a value based on experimental data. The calculation is $$k = \frac{a - b}{c} \cdot \frac{1}{T},$$ and $a$, $b$ and $c$ are all measured experimentally, multiple times, with some ...
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1 vote
1 answer
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### Calculating the value of Cox-Snell Rsquared

I want to calculate the minimum sample size for a prospective longitudinal study (using cox regression - the aim of the project is prediction). The following function pmsampsize from the pmsampsize ...
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1 vote
1 answer
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### Sample size for Survival Analysis (Cox regression) with discrete time

I have a study where the patients come to the hospital every two months for check-ups. T0 ( one week before surgery), T1 (two months after surgery), T2 (4 months after surgery) up to T9 (18 months ...
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4 votes
1 answer
123 views

### Sample size for REPEATED MEASURES ANOVA

I am calculating a required sample size for the Repeated Measures ANOVA (within subject). I came across two different packages and the results are different. Using "WebPower" package and the ...
0 votes
1 answer
32 views

### Sample size for survey

My interest is to perform a statistically significant survey on a population of 1700 people, that can be described in different categories, so each person belongs to only one category. I have two ...
1 vote
0 answers
31 views

### Random sample and its underlying sample space [duplicate]

A random sample of size $n$ is a random vector $X=(X_1, ..., X_n)$, where all $X_i$ are i.i.d., and are measurable functions on some sample space $\Omega$. Let's say, $\Omega = \{H,T\}$, i.e., heads ...
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7 votes
2 answers
298 views

### Calculating sample size for comparing pretest and post-test scores

I am trying to evaluate a new curriculum. I intend to do it by giving students a test at the beginning of the academic year (pretest) and one at the end of the year (post test). There are roughly 50,...
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### What is the meaning of confidence intervals when NOT using sample data and instead have data on the whole population? [duplicate]

I'm trying to understand why you would need confidence intervals or compute statistical tests (for comparing proportions) when your data is NOT from a sample and you have data on the whole population. ...
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1 vote
0 answers
58 views

### Robust estimation of standard deviation using relatively small sample taken from a Gaussian distribution

I'm sure this question was asked before, but I don't seem to be able to find a convincing answer. If there is a relatively small set (say 3<n<20) of observations of a quantity that is assumed to ...
1 vote
0 answers
7 views

### Clarifying between sample date and input data

I'm reading section 2.6.3 from the book "The Elements of Statistical Learning" of "Trevor Hastie", "Robert Tibshirani" and "Jerome Friedman" and I have a few ...
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0 answers
34 views

### ARIMA model underestimates

What steps should we take if my ARIMAX model consistently underestimates? Furthermore, should this underestimation be a significant concern in my analysis? Edit: I am doing an ARIMAX forecast where I ...
6 votes
1 answer
166 views

### Terminology clarification about sample moments

According to MathWorld (link): "The sample raw moments are unbiased estimators of the population raw moments". While in Wikipedia (link) it is said: ...the $k$-th raw moment of a population ...
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127 views

7 votes
4 answers
870 views

### Sample notation: When to use capital $N$ vs lowercase $n$?

In statistics and psychological research, what is denoted by capital $N$ vs lowercase $n$? I work in psychological research and I've seen them used in two ways: Capital $N$ represents the entirety of ...
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### Sample Size Calculation-Theory

thanks for all the knowledge, have learned a lot. I am preparing for the sample size calculation block in my master program and I have a question regarding the theory of it all. As a medical doctor I ...
3 votes
1 answer
58 views

### Expected value of ith sample versus expected value of a random variable

Consider a random variable $X$. When we talk about the expected value of the random variable $X$, we use the notation $\mathbb{E}\left(X\right)$. However, I found that, in introductory statistics ...
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0 answers
23 views

### Using sample at lower hierarchical level (products) to draw inferences about a higher hierarchical level (companies)

I have a conceptual question about whether we can use a random sample of products to draw inferences about companies. More generally, I think this would extend to sampling hierarchical data, where we ...
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1 answer
50 views

### The point estimate and the large sample size [closed]

My colleagues and I argued about the point estimate's accuracy. They said that "The point estimate will tend to be accurate if the sample size exceeds 30." While I am saying no, "The ...
0 votes
0 answers
24 views

### Confusion forming prior beliefs

Let's say, for the sake of ease, I have a sample of data that I believe comes from the binomial distribution. Let's say I have 100 observations in my sample. Previous to this experiment, I have ...
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0 answers
36 views

### Why are Random Variables used instead of Sample Spaces? [duplicate]

Background This is related to the following question: Is an experiment's Sample Space always useful? I have been reading about Sample Spaces, and I understand they represent all possible outcomes ...
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5 votes
2 answers
335 views

### Is an experiment's Sample Space always useful?

Background I'm working through the Harvard Stat 110 probability course. One of the first topics discussed is the sample space of an experiment. I understand that the sample space represents all the ...
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0 votes
1 answer
40 views

### Normality assumption n=48 [closed]

Regarding normality assumptions for model evaluation I have been told by my supervisor that it is not needed in the case of analyzing but is needed in forecasting only. i am looking for an explanation....
0 votes
1 answer
116 views

### How to find the correct sample size for a non parametric hypotheis test

I have two independent population data with each having 500 K rows. The goal is to perform a hypothesis test and test the claim that the new machine takes less time than the old machine. This 500 K ...
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1 vote
0 answers
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### Sample size calculator for Ordinal Data

For my experiment, I am comparing the results of melanoma grades( ordinal data, such as Stage 1, 2, 3, 4) as obtained from my proposed noninvasive imaging modality to that obtained from the gold ...
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2 votes
0 answers
120 views

### Variance of Fourth Sample Central Moment [closed]

I am trying to derive a formula for the variance of the fourth sample central moment $m_4=\frac{1}{n}\sum_{i=1}^n (X_i-\bar{X})^4$ (where $X_i$ is the $i$th realization of a random variable, $\bar{X}$ ...
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1 vote
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### Range of Subset of Population based on a Sample

Suppose I have a population with a known mean, range, and variance of a characteristic $v$. I am producing sets from this population that are of negligible size compared to the size of the population. ...
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57 views

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### Sample Size Question - Population- Multiple Regression?

I am doing a research project for class. Our research questions are as follows: Has news exposure impacted parental decision-making in preparation for the new school year? Has Media exposure to ...
1 vote
1 answer
32 views

### What are the individual elements within the outcome of a sample space called?

What is each entry in an outcome of a sample space called? For example, say our outcome is ${HHT}$, describing two heads and one tail. What is each head ($H$) and tail ($T$) member of the outcome ...
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79 views

### Closed form formula for distance of multinomial sample from underlying distribution

Suppose that I have a probability vector $p$ e.g. of size 10, and that I draw a multinomial sample of size $n$ from $p$. Does there exist a closed form formula to compute the expected total variation ...
1 vote
1 answer
11 views

### How can we use average total time if a job to determine time of components?

Imagine a scenario where there are tasks (called jobs) made of many smaller tasks (called assemblies). Each assembly has an average time to completion, and the job time to completion is a sum of the ...
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0 answers
30 views

### How to test that a sample of a discrete random variable is representative?

I am given a discrete random variable and several large samples from it. The methods how the samples are obtained are not truly random samples but are reasonable approximations to a random sample. An ...
• 488
4 votes
1 answer
140 views

### Do I need a hypothesis test to compare two populations of complete annual count data?

I would like to compare the total number of public M&A transactions observed in two separate years (e.g. 2021 vs 2022). Given the data set for each year is complete (i.e. a population), can I ...
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3 votes
1 answer
341 views

### Question about Analogy to Statistics

If anyone could help me verify if my analogy is correct, thanks so much! Here is an analogy: A population is like a pot of soup. We stir the pot of soup with the ladle because naturally the contents ...
1 vote
0 answers
44 views

### Bayesian inference on model parameters from summary statistics alone

Consider quantities $y_1,y_2,\dots,y_p$, for the $j$th of which we have $n_j$ measurements $y_{1j},y_{2j},\dots,y_{n_jj}$. Unfortunately, I do not have access to the raw data $y_{ij}$ -- only to the ...
0 votes
0 answers
58 views