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.

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Can you infer that sample is representative from statistical power?

I have travel times for 1000 routes (origin-destination pairs) and I collected about 12 actual travel time samples by driving some of these routes (randomly selected out of the 1000). I calculated ...
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13 views

How can I compare data from a sample of a population with data of that population?

I am looking at a survey and I want to crosscheck the data from the survey respondents with the data from the actual population (we have the information available) to see whether any sub-groups were ...
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1answer
134 views

Estimate variance of a population if population mean is known

I know that we use $\frac1{n-1}\sum\limits_i(x_i - \bar{x})^2$ to estimate the variance of a population. I remember a video from Khan Academy where the intuition given was that our estimated mean is ...
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23 views

Should two way anova with unequal samples use weighted or unweighted means?

My data were collected in a 4x2 factorial design with 4 sample areas and either high or low rainfall. I'm looking to carry out a two-way ANOVA but the sample sizes are not even. Should I use ...
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1answer
17 views

Determination of sample size for a proportion

SCENARIO The parent company has other business units (think of these as franchises owned by the parent company). In order to quality assure procedures the parent company samples employees’ work at ...
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17 views

Sampling non-normal (near power-law) distribution

Context: I have a population that shows three distinct behaviors (slope) on a cumulative distribution function (survival proportion over time) and I want to find factors that may explain these ...
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11 views

What does number of events symbolize?

What does number of event means? http://www.biomedcentral.com/content/pdf/1756-0500-5-52.pdf I was going through this datasheet to perform a meta analysis and found that it demanded number of events ...
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7 views

Weighting Method that preserves population proportions and sub-sample population proportions

I created a weight based on 3 socio demographic characteristics (SDC) of my data to equal known target population proportions using RIM (random iterative method) weighting. E.g. the population ...
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10 views

sample size query

I have a question regarding the sample size required for a project i'm involved in. Without going into too much unnecessary detail, we have processed 905 cases (in the last day) and 4 of them were ...
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1answer
73 views

Uncorrected sample standard deviation in correlation coefficient

There seems to be a common use of the uncorrected sample standard deviation in calculating the correlation coefficient: ...
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34 views

Sample Size for Comparing two Measuring Tools

Let's say I have two devices that measure the same thing: the thickness of an object. Knowing that device 2 is more accurate and precise, I wish to see how accurate device 1 (how close do the readings ...
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1answer
28 views

Treatment and Control group, the sample size

I am doing the evaluation for a program with 200 members (they enrolled in the program at different times in the past year and the program doesn't end). Only 78 completed the pre test survey. Now I ...
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1answer
30 views

Estimating the parameters of a Beta distribution using the sample average and standard deviation

This is a simple question, but I just want to be sure. Imagine that we have a sample of $n$ data $\{x_1, \dots, x_n\}$ and that we want to fit them to a Beta distribution. Imagine that we have ...
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14 views

What kind of delimitations belong to population and sample respectively?

I'm writing a bachelor's thesis and the research question is "How ambitious is Sweden's electronic tax return system compared to other states'?". We wanted to investigate those states which (1) ...
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1answer
351 views

Why doesn't a sample proportion also have a binomial distribution

In a binomial setting, the random variable, X, that gives the number of successes is binomially distributed. The sample proportion can then be calculated as $\frac{X}{n}$ where $n$ is your sample ...
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3answers
92 views

Enlarging a random sample

In our project we have a population of 1000+ individuals. We picked a random sample of 107 individuals, but then we realized we needed more precision, so now we want to have a larger sample. The ...
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28 views

Use a model to reduce sample size?

I have a consultant that is proposing that he can reduce my sample size by using a model that is built off of previous samples. My first response was "NEVER EVER EVER EVER DO THIS". However, after ...
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42 views

Sample size calculation for crossover design using dependent t-test - role of $\rho$?

I am trying to do a sample size calculation for a 2x2 crossover study. I have access to previous studies whereby I can get covariate adjusted estimates of the variability of the responses (from a ...
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24 views

Maximum Probability over a Random Variable's Sample Space

Assuming I have a joint probability density $p(X, Y)$, $X$ and $Y$ being continuous random variables. I'm trying to find the maximum of $p(X=x, Y)$ for a fix value $x$ but over the complete possible ...
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17 views

Error bars for the fraction of two samples

I have two samples, lets say sampleA and sampleB. I have used jackknife resampling and obtained the error bars for each of the ...
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1answer
91 views

How to extrapolate my sample results to population

We have tested randomly selected bacteria ($k = 198$) for antibiotic resistance over a period of 3 years (total isolates $n = 444$) and observed $117$ resistant strains. I would like to extrapolate ...
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24 views

Data set sample

I'm willing to make a comparative study, to examine culture dimensions effect on countries with the highest GDP and countries with the lowest GDP countries, but there is no enough observation to make ...
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0answers
29 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 ...
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1answer
28 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 ...
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22 views

variance and sample confused

When solving (b), is the variance $$ V\bigg(\frac 1 2 (x_1+x_2)\bigg) = \frac 1 4 V(x_1+x_2) = \frac 1 4 \big(v(x_1)+v(x_2)\big)= \frac 1 2 \sigma^2 $$ or should I divide the variance by the sample ...
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7 views

How can I get a confidence interval for p from a small cluster sample?

I have small cluster sample (n=4, N=75) where all elements in each cluster are sampled. I'm using a ratio estimate to estimate p, the proportion of successes. If I can't use the normal approximation ...
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1answer
60 views

Sample variance from second moment

if I have a sample composed by values lesser than 1 and i want to compute the sample variance with $ \frac{n}{n-1}(\langle x_i^2 \rangle - \langle x_i \rangle^2)$ how can i do? Because the mean of the ...
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29 views

Determining the Random Sample - Healthcare Case

How would we determine the random sample in the situation (I'll describe it more in detail now): 5 doctors, 10000 patients, average accuracy of cancer diagnosis of entire population is 0.56 from all 5 ...
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38 views

How to calculate the randomness of a sample and if it is representative on r?

I am doing a project on R commander and the project says, "The set of exoplanets discovered to this day is a sample of all exoplanets that exist in the universe. Discuss whether you think this sample ...
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14 views

a problem on sample survey

i have found this problem on sample survey in an old Indian Statistical Institute question paper. Consider a collection of $N$ cards, numbered $1, 2,\ldots,N$, where $N \geq 2$. A card is drawn ...
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53 views

What distribution is this? (and how to simulate a sample from it in R)

This is the information given: 10% of the population is colour blind. Let $X$ be the number of colour-blind people in a sample of 20. The distribution is $X \sim Poisson(20, 2)$ - is this correct? ...
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1answer
85 views

How many samples needed to determine value 4 sigma away from mean?

I have a source that generates computer files varying between 20,000 and 40,000 bytes in length. I think (strongly assume so) that they vary in length according to a Normal distribution. They average ...
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22 views

Linear mixed-effect models for variables with unequal size

as a biologist I am currently analyzing data where variable sizes are unequal but nevertheless dependent on each other. In my specific case, I am aiming to test with a linear mixed-effect model ...
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2answers
407 views

Still confused with the p-value definition

The p-value is defined as the probability, under the assumption of the null hypothesis H, of obtaining a result equal to or more extreme than what was actually observed. A p-value lower ...
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1answer
849 views

Advantages and disadvantages of using population and samples for statistics

I need to know the advantages and disadvantages of using a sample or a population to collect data. I understand what a sample is and what a population is, but I do not know what the advantages and ...
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2answers
45 views

Comparing two populations [Beginner]

I have sampled from two separate populations, and I want to figure out which population is better. Population 1 has an average score of 84.1 and a standard deviation of 11.8. Population 2 has an ...
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15 views

Filling in “gaps” in Sample data from universal data

Quick background - I have a BS in mathematics, and have just recently started a position related to data science (nothing heavy, but requires enough simple statistical analysis that I find myself ...
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1answer
84 views

Sample size and Central Limit theorem

I'm working on an example in introductory statistics and I'm not sure if my answer is correct. I think 2,3,5 is correct and not sure about 1,4. Am I correct? It's about choosing correct statements ...
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45 views

What sample size is needed to estimate the population mean, with unknown variance?

I want to know what's the sample size needed to estimate the population mean, with unknown variance? I'm filling up a database that stores the values of wifi-accespoints' strength level at certain ...
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4answers
46 views

Sample size of sampling distribution of the sample mean

When people say that the mean of the sampling distribution of the sample mean is equal to the population mean, is this true regardless of how small or large the size of the samples are? I'm having a ...
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14 views

validity when between subjects factor makes group size uneven

I'm doing a repeated measures analysis and, while I have even amounts of samples for each subject, and the variances and sphericity are fine for the dependent measures, I'm worried because I have ...
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1answer
67 views

How to create matched sample for sample selection method to perform?

I'm working on a project in which I only use sub sample (say the immigrant households of all households), and there is a sample selection problem that I apply the standard Heckman's sample selection ...
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1answer
47 views

Analyzing data while collecting the data

Part of our samlpe has been collected (Phase 1, $n=12$ subjects with measurements pre and post treatments). The remaining sample (Phase 2 with another 8-10 subjects) will be collected in a few months. ...
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1answer
107 views

Sample size for categorical data

I have a population of phone calls - 200,000. There are different reasons for each call, but lets assume the number of reasons is known. i.e. 7 different call reasons: 1) Check on order 2) Cancel ...
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3answers
44 views

Inference about parameter $\theta$ be same?

Let $\mathbf x$ be a sample point and $T(\mathbf x)$ be a statistic of $\mathbf x$. Similarly, let $\mathbf y$ be a sample point and $T(\mathbf y)$ be a statistic of $\mathbf y$. In the book ...
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30 views

How many samples are enough

I have objects with large number of attributes (about 60.000). Attributes are actually deviations of object part from model. I would like to cluster this objects, to get centroids that will represent ...
2
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1answer
70 views

Example of sample $X_1,X_2,\ldots,X_n$

In the book Statistical Inference by George Casella, it is written that An experimenter uses the information in a sample $X_1,X_2,\ldots,X_n$ to make inferences about an unknown parameter $\theta$. ...
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1answer
11 views

Test of two proportions from the same survey

I was wondering which test I should use for comparing two proportions from the same survey. Example: A survey of 1000 people ask two question. "Do you smoke everyday?" and "Do you drink alcohol ...
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3answers
128 views

Why take multiple samples from a population?

I'm fairly new to Econometrics, and I'm curious about, when trying to estimate the population parameter, why it is important to take multiple samples of the population, instead of just combining all ...
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1answer
60 views

Assessing a sample mean with a confidence interval vs a hypothesis test [closed]

I'm reading this pdf on statistics. I wanted to ask the difference between sections 3.5 and 4.2. In section 3.5 it is described how to compute, from a sample, an estimate of the mean with a ...