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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24 views

Comparison of two means

Which test should I use, if I want to compare the mean of the whole sample with the mean of the fraction of the sample? So for example the mean of the whole classroom taking the test and the mean of ...
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9 views

procedure of statistical modeling of sample

I never did the statistical modeling of sample. Usually i was engaged in common statistical procedures(descriptive statistic, correlation, regression, factor analysis and so on). Now i decided find ...
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16 views

G*Power analysis -sample size calculation

My experiment is devised as follow: There are two different types of stimuli-- cellphones: android (android-1; android-2) and iOS (iOS-1 and iOS-2). A sample size of 60 subjects are divided into two ...
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42 views

What is the difference between sample and outcome? (plus events and observations)

I was sure that these are the same things but I do not get the difference reading about mass probability function Suppose that $X: S → A (A \subseteq R)$ is a discrete random variable defined on ...
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26 views

Stratified random sampling and its distribution

I'm learning stratified random sampling and I'm having hard time to solve this problem. consider the following population of six units: ...
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33 views

Binary logistic regression: low event rate

I want to investigate how people (lets say smokers and non-smokers) differ in various characteristics. So I want to perform a binary logistic regression with SPSS. However, my event rate is very low ...
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3answers
278 views

Why cannot a sample of voluntary patients be generalized?

In the book “OpenIntro Statistics” it is specified that samples of voluntary patients cannot be generalized. Why cannot a sample of voluntary patients be generalized?
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37 views

Is it true that values of parameters do not vary from sample to sample?

This is something I was told. However, it seems to me that parameters of a population can be functions of time, in certain situations, in which case the values of parameters could vary from sample ...
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1answer
55 views

$E(X_1| \overline X ) = \overline X$, the sample mean

Let $X_1, X_2, ..., X_n$ be a random iid sample from a population with mean $\theta$. Now I am wondering about the intuition behind $E(X_1| \overline X ) = \overline X$, the sample mean. If we just ...
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19 views

When can a pilot sample be included in the main study?

For example, when estimating the proportion of database records that agree with paper documentation. Auditing each record is tedious, so it is tempting to include the pilot sample in the main study ...
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15 views

Configural frequency analysis

What do you think about configural frequency analysis? http://en.m.wikipedia.org/wiki/Configural_frequency_analysis I personally love the idea to extract types and antitypes in heterogenous samples ...
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25 views

Choosing correct statistic aproach for dropout analysis

I need some input from you. At the moment, I feel a gap opening between theoretical knowledge and practical implementation. Problem case: In my study, I did an identic training program, around 10 ...
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1answer
37 views

Variance of sample correlation coefficient

On wiki page about Fisher transformation I read that variance of sample correlation coefficient becomes smaller as population correlation coefficient (in absolute value) gets closer to 1. Could ...
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1answer
18 views

Picking the top 10 answers from a survey

I ran a survey on a population of advisors in all the different recruitment centers of in a country. I had 1410 text written entries (not multiple choice) I took a sample of 284 to see what are the ...
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41 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 ...
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27 views

Characterization of normal distribution [duplicate]

How can one prove that the random sample is normally distributed if the sample mean and sample variance are independent?
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16 views

Where can I download sample data sets for mobile app downloads?

For statistical testing, I am in need for android and apple mobile app download data. I have checked on AWS (Amazon) and Infochimps. No luck so far. Can anyone suggest other resources or is there a ...
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36 views

Random variables: True or False

I sometimes get confused when reading statistical definitions when they mention random variables (RV). Are they talking about a single draw? Are they talking about an estimator? To make things clear ...
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29 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 ...
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3answers
2k views

Is it a truly random sample?

Any hints on how to solve this problem? A sample of 400 items is taken from a normal population whose mean as well as variance is 4. If the sample mean is 4.5, can the sample be regarded as a ...
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34 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 ...
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12 views

Mixed groups of participants

It is permissible to analyse data for a group of persons, which contains repeated measures data and independent measures data. Can I analyse this data as if it comes from one group? If not why not? ...
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1answer
40 views

Finding the level of significance of a sample

I have an exercise with the following information; $ 20\% $ of the set are youth, my sample of $ 139 $ persons have $ 39 $ youths. The exercise is to test if this sample is a representative sample of ...
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1answer
41 views

How to combine sample means and sample variances?

Given a set of data, assumed normally distributed from 1 to 19. And two subsets of that data, one with the numbers below 10, and one with the numbers above: ...
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37 views

Are samples from sliding windows independent samples?

Are samples from sliding windows independent samples? E.g. if I have window size of 90 seconds counting the number of cars on a street and I output the average within the window every second for 30 ...
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32 views

Check if sample is representative of a larger sample

From a larger sample of tabular data, I have picked certain rows that meet a certain condition (this condition is unrelated to the actual data in the rows). Now, I want to know if the distribution of ...
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15 views

Can I average samples in nested factor within-subject design if samples are from the same condition?

This question relates to one of my other questions: Split plot with nested factors ANOVA in R . I have subjects taking an experiment, where I have different ...
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115 views

Estimating the size of an intersection of multiple sets by using a sample of one set

I'm working on an algorithm which needs to calculate the size of a set generated by the intersections of at least 2 sets. More specifically: $$ z = \left |A_0 \cap \ldots \cap A_n \right | $$ The ...
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1answer
45 views

bias and variance of correlation estimator

I calculated the bias and variance of sample mean $\hat{\mu}$ and sample variance $\hat{\sigma}^2$ but I could not calculate the bias and variance for sample correlation $\hat{\rho}$. How can I do the ...
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38 views

Proportionality of significance and effect size

Is it true that, given a fixed sample size N, it can be said that some measure of effect size and the measure of statitical significance (e.g., 1-p) are proportional? In other words, that, when ...
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1answer
41 views

NBA Points Per Game

I have a database with many thousands of entries of box scores. Each box score has a player name, date played, points scored, minutes played, and some other stats like rebounds, assists, etc. I want ...
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43 views

Problems with the sample (unkown population)

I realized a large research with Brazilian physics high-school teachers and I wanted that my sample could be representative of the Brazilian physics high-school teachers population. However, nobody in ...
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1answer
59 views

Combining results of two samples to find combined standard deviation

I was making an attempt to solve the following problem sets, however, my answer 15.913 seemed quite different from that in the answer key 16.84. I have checked my answer a few times and re-doing the ...
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1answer
32 views

Can Inferential Statistics be carried out in a Retrospective Case Study?

Just wanted to check with regard to a retrospective case study, if various data is collected for a set of patients on different variables can this be interpreted with inferential stats tests? Even if ...
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14 views

How can I determine the probability that a sample has a certain average given details about the total population?

Imagine that I have goal scoring data for a hockey team. They average 2.43 goals scored per game with a standard deviation of 1.63 for this data set. They have played 82 games. I have two subsets of ...
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12 views

Computationally cheap estimation of the mode from 2D samples

I say 'mode' in the title – perhaps there's something more appropriate I can find. Here's my problem: A person is in a $100\mathrm m$ by $500\mathrm m$ space. I have about 100 samples randomly ...
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14 views

How to cross validate with optimal sample size selection?

My problem is as follows: I got a training set composed of texts, where 10% of observations are 1, and 90% are 0. To make it simpler, lets say that 1000 is 1, and 9000 is 0. I implement Naive Bayes ...
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1answer
48 views

Maximum likelihood of two Poisson distributions

Suppose I have two sets of samples $\{a_i\}$ for $i=1, \ldots, n_a$, and $\{b_j\}$ for $j=1,\ldots, n_b$, drawn respectively from two Poisson random variables $A \sim\textrm{Poiss}(\lambda_a)$ and $B ...
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2answers
63 views

Where is traditional inference really relevant?

I have been occupied with a fairly simple question regarding ordinary inference procedures where my own, and many others, practice feels slightly uncomfortable. We know that the purpose of ordinary ...
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1answer
95 views

Way to correct sample selection bias with unknown selection?

I would greatly appreciate some advise on a statistical problem that haunts me. Suppose you wish to estimate the effect of $x$ on $y$, but the probability to observe $\{y_i, x_i\}$ also depends on ...
2
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2answers
121 views

Z-scores, standardized tests and population means

I have been using z-scores by subtracting the mean (and then dividing by the SD) of the sample, whereas I recently read they actually need to be the population mean and SD. Assuming you are ...
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51 views

Term used to describe a particular sample

Suppose that we know that captured data follow a particular distribution. We have 10 sample. 9 of them are close to the supposed distribution but the last sample seems to be very distant, or event ...
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50 views

What is the Australian Calculator?

i need to know how to use the Australian Calculator to get my sample size. i was instructed to carry out my research using the Australian Calculator, but i don't know what it means.
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305 views

Expected standard deviation for a sample from a uniform distribution?

I've been trying to find information on the sampling distribution of the standard deviation for uniform distributions and have been having a heck of a time figuring out the expected value for the ...
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17 views

Sample/Null Value

I was running through question section on my stat book and the following question was posed: If our sample value is close to the null/population value, we conclude that ... I don't get if that ...
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1answer
41 views

Kolmogorov-Smirnov with parameter estimates

Can someone explain in as clear a (formalish mathematical) way as possible why the KS test in original form with parameter estimates is unreliable?
2
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1answer
56 views

Validating a Data Set.. Which Test should I use

I have a data set(size around 1000) which was collected by a third party. I want to verify the correctness of this survey data using random sampling (by telephoning). Is this a correct approach to the ...
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1answer
115 views

Sample from a custom continuous distribution in R

I have a probability density function in R and I want to draw a single sample from it. How do I do that? My current solution (and the one Google keeps giving me) is to evaluate the function for a ...
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15 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 ...
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27 views

Interval regression with sample selection in Stata

I'm wondering if anyone knows how to correct for sample selection when using the interval regression, preferably with Stata. I have firm-level bribery data of which 70% did not pay a bribe. For the ...