A population is the entire set of units from which a sample may be drawn.

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Sample Representing a Different Population

I have two sets of populations: containing 1.5 million and 5.5 million units. I need to select a sample out of 5.5 million population so that the sample represents the 1.5 million population based on ...
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7 views

Estimating variance or coefficient of variation for population given total and count for four segments of population

My goal is to estimate the coefficient of variation for a population, but the data we have been given is very limited. All we have is the total and count for four segments of the population. The ...
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16 views

Do I have to test normality for both groups when comparing from a single population?

This should be an easy one. I'm a novice when it comes to statistics and English isn't my first language so bear with me. I have one population that numbers about 700. Of these 700, 25 are of special ...
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13 views

Understanding sample and population (real life scenario)

A real life case: a firm desing, produces and sells 52 vehicles. I collect failure data of the components of the vehicles. after a time, -for example- for the oil filter I have 52 data. Some of them ...
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48 views

Uses and estimation of Student-t distribution

My question relates to a confusion between how the Student-t distribution is often documented versus how it is used. In the documentation the Student-t is used (from Wikipedia): when estimating ...
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18 views

help me choose statistical analysis for my undergrad thesis [closed]

firstly, i'm sorry if i'm not very good in statistics, i just need to finish my undergraduate thesis, but my professor is very busy, that he always don't have time for me to consult my research. so ...
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19 views

Skewed population example

"Consider a strongly skewed population (e.g., waiting times at airport security screening)." My book always uses that example when referring to skewed populations. I don't understand why would ...
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29 views

Population vs sample

When we think of linear regression, the implicit assumption is that we only observe a small fraction of a possibly infinite large population. Thinking of simple averages, imagine a fair die. The ...
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19 views

Estimating actual score from small sample when population known

My inclination here is that there's no statistically sounds way of doing this, but I want to verify this. Suppose you have a population P, and you are measuring test scores across the population such ...
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27 views

Sample similar to Population

I have 100,000 customers, each customer has a few variables associated with them, separated into 100 groups. I want to find a sample of 10 groups that best represents the entire 100 groups. What are ...
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7 views

Statistical Data Changing Over Time

I am attempting to determine voter registration rates by race within specific precincts in my county. The local Supervisor of Elections' Office provides data online of the voter registration rates by ...
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1answer
33 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 ...
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24 views

Homework: Population mean inference with unknown standard deviation

I am doing my homework on population mean inference with unknown standard deviation, and I hope I could use your help with this one particular problem: During one week in January, OfficeMax ...
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15 views

Sample size for entire population to determine sub population?

Let's say a bus company has 500 markets with an average of 10000 passengers each day but some markets as large as 100000 and some as small as 300. How would I determine the simple random sample size ...
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18 views

Assessing effect of sample in its population

I have population of 200 people with their BMI . I want to remove 30 people of similar characteristics from the group and see if that makes any statistical difference on BMI of population(now 170). I ...
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13 views

Determine Number of Users in Control and Treatment Groups

I need to be able to determine how many users should be in a control group and how many users should be in the treatment group. I have read that it is statistically best to split it 50/50, but with my ...
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34 views

Standard Deviation of Averages

Any help would be much appreciated: My data is grouped into 42 categories according to classification of bird catch. Each group contains "X" amount of species, but for ease of input we categorize ...
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51 views

How to assess the probability that a sample belongs to a known population distribution with prior information on block design?

I would like to assess the probability that a sample belongs to a given population, but accounting for prior information of the study design. Short description of the study: I have a large area ...
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12 views

Identify suspect changes within a population

I am looking for a method to identify suspect changes within a population. Let's suppose that I have a database with information on 1 million Chinese companies, including information on the ...
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3answers
91 views

Sample size in a population of 300

I have to conduct a survey in the discipline of International relations. I have a list of 300 diplomats to interview for close ended, open ended questionnaire. I want to select randomly every fifth ...
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21 views

Different correlation inside groups with same population

I'm analyzing data from >100 subjects randomly assigned to two groups. Each subject has a skill level and a self-evaluated skill level (the latter being the subject's own perception of the former). ...
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13 views

Removing observations from sample & extrapolation

I have a survey that was administered once to establish baseline, and again to follow up. The baseline was created from a random sample of the population (1,200 respondents). The follow up survey ...
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22 views

Model selection for differences in outcome (binary) across groups?

The problem: A group of agencies (n ~ 20) performance varies significantly on a binary outcome from 0% to 100% (both with small n, more commonly from 20% to 60% for larger n agencies). Is this an ...
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17 views

When drawing numbers from a population how to determine if the population shifts over time?

I administer technical interviews for a programming position. During the process I generate a single number 0-12 for each applicant's likelihood to succeed within the company. Over the last year I ...
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5 views

Expected rates when scalars that describe populations are not necessarily applied to mutually exclusive members?

So, I was reading a biology textbook, and it talked about how the liver recycles half of its macromolecules a week. It got me thinking really hard about a specific scenario. Assume you have $n$ ...
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14 views

Estimate population parameters base on two-level random sampling

I have a general population(N) and then random-sampled n samples from N. For each individual object in the samples, I random-sampled 1000 activities(for example, let's say 1000 "online display ads") ...
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18 views

How much weight should be given to sample mean as an estimate of the population mean?

This R code creates a population of size 10,000 with a population mean of 3 and a population standard deviation of 2: population <- rnorm(10000, 3, 2) We can ...
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57 views

Forecasting - Population Death Rates

Wondering if you can help me out with this problem: I have 2 closed populations of products (call it Product X, and Product Y). Population Size of each product 10 million each (Product X = 10 ...
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48 views

Significance test for subset variation from population

I have customer churn data: independent features like customer gender, location, age etc. outcome feature representing whether he/she has churned or not My population churn rate is around 30% ...
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296 views

T-test for Bernoulli Distribution- Sample or Population data for SE calculation?

Am struggling to understand part of the answer to a question have done- Qu- In a given population, 11% of the likely voters are African American. A survey using a simple random sample of 600 landline ...
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12 views

Something confused about parent population and sample space

My text book proclaims that iff there is exact one element in each sample, then sample space is equivalent to parent population. And I think it's not correct. For example, let parent ...
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31 views

Comparing results of surveying two different groups (of the same size)

I have surveyed two groups of people. They had option of answering one of three questions. Both groups picked one of the answers around 50 and 51 percent of time. How do I compare if this difference ...
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7 views

Comparing a sample's mean to the population's mean from which it was taken

Let's say I had Population A (N=1200). Population A is composed of 1200 Sample areas each with their own mean/SD, etc. Let's us assume that taking all of these Samples together is the entire ...
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23 views

what's the right way to combine binomial parameter estimates?

let's say you have a bunch of weighted coins. by observing flips, you can estimate (a confidence interval for) the binomial parameter for each. how should you combine these to summarize the ...
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25 views

How do I calculate needed sample size

I am measuring visitors to a website in an A/B test (i.e. showing two different versions randomly to visitors and comparing what % converts). I am trying to calculate an estimate for what sample size ...
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72 views

WEKA accuracy confidence interval

I have a dataset consisting of thousands of companies from the UK. For 300 of these companies, I collected several indicators which were extracted from social media (e.g. #likes). I have built a model ...
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25 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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99 views

Defining a Population

I am tracking monthly data entry errors in a customer service dept. of 20 people, and then doing regression and correlation analysis on variables like typing speed and data entry error. I have data ...
2
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58 views

Estimating frequencies of a population

I have a sample of size 1121 from a population of size 2171 and I don't have access to any additional samples. The counts are ...
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14 views

Is using the whole population and sample data as a co-variance in spatial analysis correct?

I have two datasets that I am using to fit a spatial regression model. One is from the whole population (say means of bike usage in each state), and a sample population (statistics means of those with ...
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22 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) ...
6
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1answer
328 views

What is exactly distributed according to t-distribution?

I try to understand the idea behind the t-distribution. Here are the steps that I have understood so far: We use a sample of N elements to estimate the population mean. In more details, we use the ...
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584 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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377 views

How to compare percentages for populations of different sizes?

I have several populations (of people, actually) which vary in size (from 5 to 6000). I would like to visualize the ratio of women vs. men in each of them so that they can be compared. I will get, for ...
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2answers
102 views

Restoration of gender balance after wars - what principle underlies this?

I am wondering what is the statistical principle that underlies the following observation. After every war in history, the male population of a given region would severely decline, tipping the ...
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36 views

Using population as weights in regional-level data

I'm analyzing regional-level data (variously at the level of metro, micro, and county levels depending on their economic integration/population agglomeration). I'm using STATA 12 SE. It seems ...
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1answer
56 views

How to scale up mean/variance and confidence interval of clinical trial for whole population

In a clinical trial I have 1000 patients with disease A. Their mean treatment cost is 1000$ per patient with a 95% confidence interval of [900;1100] for example. The whole population of country X is ...
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23 views

How can test corpora (with different sizes) be compared to each other via accuracy?

I need an advice regarding a text-classifiction scenario. I use a simple accuracy measure defined as #(correctly classified classes in a corpus X) / #(all docs in X). Let A, B and C be three ...
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56 views

Choosing right test to compare two populations

I have two populations whose size is 36 and whose values I want to compare. Example ...
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11 views

Could someone verify this logic for managing probability distributions in experiment samples?

I'm not well versed in stats lingo, but am hoping my logic in the concepts here makes sense and is correct. Often in my work (measuring electrical responses of cells) I take of more than one ...