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.

learn more… | top users | synonyms

1
vote
0answers
22 views

How can I calculate ± estimate based on sample set?

Say I have a completely random sample of 25M weights of a population of 100M. Say the average weight of the 25M random sample is 150lbs with a standard deviation of 45lbs. How can I be more precise in ...
0
votes
0answers
29 views

How to determine if sampling is representative/similiar to my population

Let say for whatever reason I have obtained a sample of an initial population. (ie. we have paired case:controls on a set of confounders). I wish to compare how representative my sampled (or let me ...
3
votes
1answer
40 views

Proving a property of $(n-1)s^2$

I would appreciate your help as I climb the stats learning curve! I want to prove the following: "Let $x_1, x_2, ... , x_n$ be any numbers and let $\overline x = (x_1 + x_2 + ... + x_n)/n$ Then ...
0
votes
0answers
6 views

Splitting an i.i.d. sample in two by criterion - what survives of independence and population representation?

Assume that I have available a $k$-dimensional i.i.d. sample of size $n$, collected in the $n \times k$ matrix $\mathbf X$. Each column represents a series of realizations from a random variable. ...
0
votes
2answers
25 views

Independent or Dependent Samples

I want to perform a statistical test: Wilcoxon Signed Rank Test to test if there is a significant difference between them, but I don't know if the two samples are dependent or not? Context: I have a ...
0
votes
0answers
10 views

how to deal non response in simple random sampling if sample saize is about 380? [closed]

How to deal non-response in simple random sampling when sample size is 380 from about 20000 population
0
votes
0answers
2 views

Independent or dependent sample in content analysis

I am conducting a quantitative content analysis on specific crime news reports and want to explore difference in the quantitative amounts of coverage depending on whether the victim was male or ...
0
votes
0answers
19 views

Problem with sample function in R [migrated]

What I'm trying to do is use the sample function in R to split up a sequence of numbers into several equal parts for later use, but I'm having a hard time not getting repeated digits even when I ...
0
votes
1answer
23 views

Are the Observations in A Random Sample Independent?

guys. I am learning the t-test on my own. The assumptions of t-test have been confusing to me. The assumptions included "A random sample is used" and "The random sample is made up of independent ...
1
vote
0answers
10 views

Compare scores calculated for two groups who overlap?

I have three groups of ten children (A, B and C). They are each have different treatments (the treatments are to do with how they are taught about a certain biological feature). Two scores are ...
0
votes
0answers
4 views

Algorithm for ranking population elements based on occurrences and sample ranks

I have a finite pool (population) of about 10000 elements. Samples of 100 elements are randomly chosen, and each sample is then ranked based on random element attributes. The 100 elements are then ...
1
vote
0answers
20 views

Stratified sampling when creating a test/training set

I am creating a dataset that I am going to use as the training/test sets for a supervised classification problem. The problem is to identify quotations in a large corpus. I have randomly sampled the ...
1
vote
0answers
13 views

How well does sample average range estimates sigma?

Suppose there are m subgroups of n items each. The following practice is described by Montgomery in the construction of a $\bar{X}-R$ chart: Let $\bar{R}$ be the average range of the m subgroups. ...
0
votes
0answers
36 views

Proportion Sample Size Estimation? Cluster Sampling

I was asked by someone running a food drive to help with the following problem: Food is being collected in bins, which hold about 1,500 lbs of food each. They are looking to collect about 500-600 ...
0
votes
0answers
22 views

Determining the required sample size to meet a bound

A company produces a special kind of utility terminals. It has N = 26016 such terminals out in the field in some city for many years. Over time these utility terminals go bad. The company decides to ...
0
votes
0answers
11 views

Estimating Distributions of Weighted Data

I'm trying to build a bivariate copula-based model of income and wealth in Italy and I'm having trouble handling weighted data. I have access to micro data, a survey of about 10,000 households that ...
1
vote
0answers
19 views

Sampling size question [closed]

I wanted to know the sampling size of a population where size is low and moreover it doesn't follow a normal curve. Moreover I wanted to roll out quality numbers at monthly level as the weekly level ...
1
vote
0answers
44 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 ...
0
votes
0answers
32 views

Good algorithm to compute the sample mean and variance [duplicate]

I am looking for good (fast, memory efficient, ideally one-pass) algorithms to compute the sample mean and variance. I have found a technical report by Chan, Golub, and LeVeque from 1983 with ...
1
vote
1answer
40 views

Pool data from two different points of time with different attendants

I have two samples (each nurses) one from 2008 and the other drawn 2013. Both got the same questionaire to fill out. Now I would like to pool the data but do not know if I just can do it. My idea was ...
5
votes
3answers
117 views

Overview of predictive modelling, machine learning, etc.

My text Intuitive Biostatistics is a nonmathematical explanation of conventional statistics. Chapter 3 explains the basic mindset of statistics as analyzing a sample to make inferences from a ...
2
votes
1answer
73 views

Sample size choice with binary outcome

Our civic association is planning to implement a survey asking our neighborhood one true false question. I would like to make sure that we obtain an adequate sample size. Let's assume N = 2500 ...
0
votes
0answers
17 views

Census Data for Regression model: American Community Survey or 2010 Decennial?

I have a data set that contains electricity use for 2012 aggregated to the city level for a number of cities in the United States. I was interested in doing some analysis to see the relationship of ...
1
vote
0answers
11 views

Parametric Bootstrap to determine sample size capabilities

I'm pretty new to the world of Statistics, so perhaps my understanding is lacking, but I'm interested in testing the capabilities of a smaller sample size in resolving a population mean. My thinking ...
0
votes
0answers
20 views

How to determine if sampling is representative to population

Is there any coefficient or some metric that will tell how well sample reflect the population?
0
votes
0answers
12 views

How to estimate the reliability of an exhaustive list of data?

I have a purported exhaustive list of beneficiaries under a social security scheme. My question is how large must be the sample of this population must be tested to check for fraud etc to derive an ...
0
votes
1answer
24 views

Is sample standard deviation a valid approximation of population standard deviation for z-scores?

Given a Normal distributions for the population and my sample, a population mean of mu, and a sample standard deviation of s, if I want to find the area under the population curve from x to infinity, ...
0
votes
1answer
21 views

Compare standard devation between different samples?

I am calculating standard deviations $\hat\sigma_i$ from many samples from distributions with mean equal to zero but different variances $N(0, \sigma_i^2)$. Each sample has different size $N$. When ...
0
votes
1answer
43 views

R how to get same sample size from different categorical values [closed]

I have an unbalanced set of records for different values of a categorical variable as shown below: ...
5
votes
1answer
85 views

Sampling 100000 times from normal distribution in R : strange distribution of samples' standard deviation

I generated, in R, one hundred thousand random samples of ten values from the normal distribution with mean zero and unit standard deviation, and registered each mean and standard deviation, in hope ...
3
votes
2answers
222 views

Population vs. Sample [duplicate]

Can you use population to refer to a particular population? For example the population of women in Maths Class, from which we can take a sample to measure the height in order to make a judgement of ...
3
votes
1answer
38 views

What is the difference between standard error and margin of error and when to use which?

Will someone please explain what the difference is between standard error and margin of error and when to use which? I have not had luck finding a simple explanation on the differences anywhere on the ...
2
votes
0answers
46 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 ...
0
votes
0answers
25 views

The sample size of a study is reduced. Is it still representative?

If the size of representative sample is lowered due to some genuine causes (e.g time, budget), then what are the possible ways to make it a representative sample within the decreased size.
0
votes
0answers
11 views

Help me inform multiple regression coefficients with additional dataset

I have a data set with 24 year on year observations. That is for a single company. I have around 500 companies with incomplete datasets (i.e. with missing values). I am trying to predict a Y ...
4
votes
1answer
32 views

Difference between errors and residuals. What is the mean and variance of each of them?

Suppose there is a simple linear model $y=\beta_0+\beta_1x+u$. Can we state that $\bar y=\beta_0+\beta_1 \bar x + \bar u$? I have this question because I come up with $Var(\bar u)$ when doing some ...
0
votes
0answers
13 views

Sample representativity and size in correlational studies

I’m in a department where our colleagues have some old-fashioned ideas. We always have a problem regarding the size and representativity of the sample for correlational studies. When I do an a priori ...
0
votes
0answers
7 views

Index A Sample Against A Population

I have a population broken down into four mutually exclusive groups of 1,000 people each. I'm recording the number of times people from each of those groups visit a store. For instance, group A has ...
0
votes
0answers
37 views

What is a sample from k-fold cross-validation run - for ANOVA

Required for assignment: k-fold CV comparing performance different neural nets (models?) There are several experiments, the biggest has 8 models (cases?) to compare. I would like to try ANOVA to ...
0
votes
0answers
28 views

How many samples are needed to determine the accuracy of a predictive model?

I'm working on a research project on education, which requires that I estimate 'average' schools scores. I have a ranking (based on several school quality measures) of roughly 1000 schools, and I ...
0
votes
1answer
19 views

is there a meaningful interpretation of the significance in cross-country correlation?

By cross-country meaning we are not sampling countries, but using the whole "population of countries" in the analysis? More generally, should one report the p-values in analyses where the cases are ...
1
vote
0answers
10 views

Testing two groups of subjects (same population) -> increased replicability?

I've seen several experimental psychology papers arguing that, because they separately tested two cohorts of subjects, that this increases the replicability of their finding. Is this really the case? ...
1
vote
1answer
32 views

How does one find the sample median of for a group of iid random variables with Laplace distribution?

I know a median is $$\frac{1}{2} = \int_{-\infty}^{\mu} f(x)dx$$ I understand how to solve this for simple distributions. However, I am learning how to do it for iid samples, which I haven't done ...
0
votes
0answers
22 views

How to test statistical significance to prove that a particular technique estimates a variable better than another technique?

Suppose the following is the scenario: I am estimating the measure of a construct. I have Subject Matter Experts (SME) who have manually (through observation) estimated the measures. Suppose I have ...
0
votes
0answers
9 views

3-arm RCT with black vs white comparisons

I am trying to design a 3-arm randomized controlled trial - intervention A for group 1, intervention A+ B for group 2 and control group for group 3. I would also like to look for black vs white impact ...
0
votes
0answers
31 views

Sampling rate and regression

I am interested in developing a regression model. The data (about 1000 observations) that I have are not really random (i.e., spatially, the closest ones are correlated to some degree), so I drew a ...
1
vote
1answer
38 views

Check population randomness in an A/B test?

I am fairly new to A/B testing and I don't really understand some points that my colleagues make. On our website users are randomly assigned to A or B when their session start (by randomly assigned, ...
4
votes
2answers
89 views

Sample mean and variance independence in the case of correlated observations

Are the sample mean and sample variance of correlated normal observations independent? The classic theory relies on the independence of observations, but this is not the case. So as an example I ...
1
vote
0answers
45 views

Understanding Chebyshev rule

http://www.stt.msu.edu/users/makagon/2.5-7.pdf For any data set, the proportion (or percentage) of values that fall within $k$ standard deviations from mean (that is, in the interval $\bar{x} - ...
3
votes
0answers
37 views

SD probability problem involving chi-square distribution

Preparing for an exam in statistics, I have been pondering the following problem: Given that in country X 14 % of people hold a university degree, find the probability that for random sample of size ...