Questions tagged [sample]

A sample is a subset of a population. Statistics, in general, is concerned with using samples to make inference about the parameters governing a larger (possibly infinite) population.

267 questions with no upvoted or accepted answers
Filter by
Sorted by
Tagged with
4
votes
0answers
127 views

Compute (bootstrap?) expected difference between two samples

What would be the correct (most statistically sound) way to tackle the following problem: Given are two samples (or empirical distributions) from two unknown distributions $X$ and $Y$, with $N_x$ and ...
4
votes
0answers
237 views

Samples size with sample proportion close to 0 or 1

For a future monitoring program on small water bodies we want to calculate the sample size. The bodies of water are so small that their number easily exceeds 100.000 in the monitoring area and ...
4
votes
0answers
126 views

Does this sampling without replacement have a name?

There can be many ways and ad hoc variants to perform sampling without replacement from a limited population. Consider we have $k$ categories (types of objects) and the k-length vector of their ...
4
votes
0answers
155 views

The practical use of the lower/upper semivariance adaptation of Chebyshev's inequality for sampled data

The wikipedia article about Chebyshev's inequality also lists a one-sided sharpened variant, based on upper/lower semivariances. It is additionally mentioned there there that "The inequality with the ...
4
votes
0answers
754 views

Measure of similarity between two multivariate samples

I have two samples from a multivariate distribution. One is approximate and the other is exact. My aim is to measure the similarity between the approximate sample and the exact sample. In particular, ...
4
votes
0answers
798 views

Weighted sample covariance

I have read the Wikipedia article, and know that the unbiased weighted sample covariance matrix for the row vector $\mathbf{x}_i$ is $$\Sigma=\frac{1}{\sum_{i=1}^{N}w_i - 1}\sum_{i=1}^N w_i \left(\...
4
votes
0answers
63 views

Difference between sample and sequence in Law of Large Numbers

I'm comparing the Chebychev (Weak) Law of Large Numbers (LLN) to the Kolmogorov (Strong) LLN in an econometric textbook and both definitions start off differently. The Chebychev LLN begins with If $...
3
votes
0answers
49 views

“Unselected sample” vs “random sample”

I've just encountered the term "unselected sample" for the first time, which seems to be fairly commonly used in medicine. Example usages: Climacteric symptoms in an unselected sample of Swedish ...
3
votes
0answers
27 views

Increase the number of samples when the PDF is invariant

Background: $$\frac{\partial C}{\partial t} = D \frac{\partial^2 C}{\partial x^2}$$ is given by Fick's second law, in which $D$ is the diffusion coefficient. The solution to this equation (given the ...
3
votes
0answers
109 views

Why don't we use the n-1 correction for standard error of sample proportion?

From my understanding, when we construct a confidence interval for a sample mean with a sample size of n, we try to estimate the standard deviation of the sampling distribution $$σ_{\overline{x}} = \...
3
votes
0answers
37 views

Does sampling fraction matter for McNemar's Test?

For McNemar's Test, does the sample need to be less than 1/20 of the population if the sample is without replacement? If so, can I correct for a sample that is larger than 1/20 of the population by ...
3
votes
1answer
193 views

Population, sample and model

Background: In Statisical Methods by Pfaffenberger and Patterson, they say that "A parameter is a numerical measure of a population characteristic." (p. 306) "A statistic is a numerical measure ...
3
votes
0answers
141 views

bound on expectation of a two-variable function under an independent distribution

Consider a probability distribution $P(x)$, a set observed samples $S = \{x_1,\cdots, x_n\}$ where $x_i \stackrel{iid}{\sim} P(x)$ for $i \leq n$, and a symmetric function $h(x,y)$. How can one ...
3
votes
0answers
153 views

How to evaluate similarity of datasets based on summary data?

I have summary data that I want to compare to my own data. For the summary data I do not have access to the underlying data, however, I know the percentiles as shown below (A). I also calculated ...
3
votes
0answers
62 views

Estimating the mean from knowing the first n largest values

There is a sample of n values that are the first n largest values of a population. Is there a way of getting any statistic such as mean or dispersion from such piece of information provided that the ...
3
votes
0answers
286 views

How to calculate the 'loss' in information when decreasing sample size?

I have a questionnaire with ~40 questions where the respondent answers on a scale 1-7 on each question. At the moment we have a sample size of say 10,000 people. The question is how I calculate the ...
2
votes
1answer
47 views

How to estimate log-normal distribution parameters from a set of data?

I don't have any background in statistics, so maybe I may say things that are incorrect. I have to model the production of waste deposition at each container of a set of containers and I have access ...
2
votes
0answers
16 views

Expected standard deviation of probabilistic sample

Let's say I have a collection of $n$ individuals, each individual is associated with a single value $x_i$, with $i = 1, 2, 3, ... n$. I now gather a sample of $s$ individuals from this collection, ...
2
votes
1answer
21 views

Logit regression (Panel data): resample?

I have a panel data (all listed companies in the US with quarterly data) in which the dependent variable is 1 if the company was recommended on a investment recommendations website, and 0 otherwise. ...
2
votes
0answers
35 views

Unbiased Estimator of the Standard Deviation of the Sample Standard Deviation

I'm looking for an unbiased estimator of the standard deviation $\text{SD}(s)$ of the sample standard deviation $s = \sqrt{\frac{1}{n-1} \sum_{i=1}^{n} (x_i - \overline{x})^2}$. I have found this ...
2
votes
0answers
38 views

Why is unbiased estimation from a sample only possible for certain properties?

I was thinking about finding some monotonic measure of entropy of a sample from a continuous distribution (2D, btw), but couldn't think of any such without making assumptions. Why is it that one can ...
2
votes
0answers
66 views

Time series: sample vs. population, population vs. realizations of random process

Suppose we have 120 monthly observations (Jan 2000 - Dec 2009) of unemployment rate and suppose we would like to use these in order understand the unknown underlying stochastic process that generated ...
2
votes
1answer
16 views

Evaluating usefulness of estimations of a parameter for different distributions

If I had a sample of size n and wished to estimate some parameter, say p for two different distributions from the produced sample what would be required to determine which was more useful? Assume the ...
2
votes
0answers
18 views

Sample size for comparing two properties of time series data

I have a dataset of observations of two properties of an object (x and y), which are distributed over time, ...
2
votes
0answers
58 views

Can we sample from a set of biased samples to get unbiased samples?

This is a follow-up question to How to uniformly sample vertices from a large graph with given distance from a fixed vertex?. Suppose I took a set $B$ of $n$ samples from a large but finite universe $...
2
votes
0answers
78 views

Construction of i.i.d. sample

My task is to describe the construction of i.i.d. sample $\mathbf{X} = (X_1, \ldots, X_n)$ where random variables $X_1, \ldots, X_n$ should get the predefined univariate distribution $P$. Specifically,...
2
votes
0answers
18 views

What is the effect of more than one chance of selection when sampling?

I am designing a clustered sample. Within each cluster there are 3 groups that will be sampled from - two at a higher rate than the other. The two subgroups that will be sampled at a higher rate are ...
2
votes
0answers
948 views

Unbiased estimator of standard deviation. Simulation results

As an exercise I decided to check if unbiased estimator of standard deviation of sample is giving better results than biased estimator . So far it looks that only in aprox 55% cases. Am I doing ...
2
votes
1answer
131 views

Population or Sample Standard Deviation: monthly climate data

I have daily mean temperature values for every day of every month for 90 years. I want to figure out: "SD$_m$": the standard deviation of daily temps across all days in a given month, for each month ...
2
votes
0answers
51 views

What are good ways to compare how “representative” a smaller sample is compared to a larger sample from which it was taken?

So basically, we have a sample of known data taken from a larger sample of known data. Is there a good way to measure how "representative" that data is, especially in distributional terms, compared to ...
2
votes
0answers
126 views

What are the sample size confidence interval calculations for the Agresti-Coull and Wilson methods for finite populations?

There are formulations for the calculus of the sample size based on Agresti-Coull and Wilson confidence intervals for infinite population in some works (like Piegorsch - 2004). However, I didn´t find ...
2
votes
0answers
206 views

For boostrapping: stratified or cluster sampling?

I am trying to apply bootstrapping on several regression models to obtain SEs of parameters. My question is about preparing the bootstrapping samples in proper manner. The data I am working on are ...
2
votes
1answer
22 views

Make inference on overall density of duplicate records from a sample

I have a file, typically of several million records, for which I need to make an inference on the percent of duplicates (perhaps testing for whether the rate exceeds a certain percent, or just coming ...
2
votes
0answers
72 views

biological sample size when instrument accuracy is weak?

I'm using a porometer to measure the transpiration of grape leaves. Unfortunately, the instrument's accuracy is 10% and it has a relatively slow (60 seconds) round trip time to produce readings when ...
2
votes
0answers
249 views

Distribution of the sample mean of a Rayleigh random variable

Let $\{X_1,X_2,X_3\ldots,X_n\}$ be a random sample from a Rayleigh distribution with shape parameter $b$. Let $\bar{X}=(1/n)\sum_{i=1}^nX_i$ denote the sample mean. QUESTION 1: What is the ...
2
votes
1answer
119 views

What can be inferred from Simple Random Sampling?

Suppose I have access to a population data set. I then perform Simple Random Sampling on this data set to pull a sample. I perform some tests to see if the population data set and the sample data set ...
2
votes
1answer
138 views

Is this considered a random/probability sample?

a company that conducts face to face surveys have described their sampling procedure as follows: We use a unique and rigorous sampling method - a form of random location sampling, using a control ...
2
votes
0answers
33 views

Making Inferences from a sample

I am trying to teach myself basic inferential statistics by going through online video lectures. However there are some gaps in my core concepts. I have a couple of quick questions Assume I take a ...
2
votes
0answers
37 views

Weighted measures in surveys

In sample surveys a weight is typically calculated so that the weighted population measure by certain pre-selected categories (e.g., gender, age groups, geographic areas, etc.) match national total ...
2
votes
1answer
219 views

Confidence intervals for percentage share of multiple response

If I have a sample of 100, who give responses to a set of multiple response variables, say for example, the brands they have purchased in the last 12 months. How can I calculate the confidence ...
2
votes
0answers
788 views

(Pretty) large sample size, unequal variance, unequal sample sizes, non-normal distribution. T-test alternative?

So, I've never had all these problems at the same time before, but I have: - Likert data, from a 9 point scale - n = 317 v 177 respectively - SD = 2.08 v. .274; 1.9 v. 2.6; 2.5 v. 2.9 etc. (you get ...
2
votes
0answers
69 views

Accuracy of approximation to sample median

Suppose we sample $n$ real numbers uniformly on $[a, b]$. We wish to find the sample median, but we will approximate it as follows: randomly choose a subset of the sample of size $k$ with uniform ...
2
votes
0answers
60 views

Why is the every data item in a sample is considered to be produced by a different random variable?

In the stats book I am studying, while explaining bias and mean, the author goes like this: "... Suppose a sample $$S=(X_1, X_2,...,X_n)$$ has been collected. ... Sample mean $\bar{X}$ estimates $\mu$...
2
votes
0answers
111 views

Need Help w/ Research Proposal

I am currently doing a master's research proposal (experiment hasn't been completed yet) and need to decide what statistical test to use. My research question is observing increases in bowling ...
2
votes
0answers
75 views

Sampling Size for a large Dataset

I am having a dataset of size upwards of 200 million rows. I have no knowledge of the distribution of this dataset. Would like to perform some analysis on this - like look at the ...
2
votes
0answers
38 views

How to simulate a sample with density $f^p / \int f^p$?

Given a density $f$ (or given a $n$-sample $X_1, \ldots, X_n$ with density $f$), is there a way to create a $n'$-sample $X_{p,1}, \ldots, X_{p,n'}$ with density $f^p / \int f^p$, where $p \in \mathbb{...
2
votes
0answers
75 views

Determine how much and why a sample differs from its population

I'd like to be able to determine a) how much and b) why a non-random sample “differs” from the population (there's probably a better word than “differs”; I was tempted to use “does not represent” but ...
2
votes
0answers
74 views

Is a sample of 1961 people out of a population of 225,000,000 a sample size that is too small? If so, why?

I am working by a set of problems on a single question in my textbook. The question explained that there was a recent survey of 1961 adults out of a population of 225,000,000 and asked me to construct ...
2
votes
0answers
25 views

Analysis of model input resolution

I am using a fine resolution soil dataset to run a climate model, and want to explore the impact of aggregating the soil properties at different resolutions on model output. E.g. how do the results ...
2
votes
0answers
70 views

Conditions for conclusion

A study had shown that annual income on average was significantly higher among men than women for people over 30 years old in Portugal. The results were from 312 Portuguese men and 62 Portuguese women....

1 2 3 4 5 6