Tagged Questions

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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14 views

What is a draw from a Dirichlet Process?

I know a draw from a K-D Dirichlet distribution is a probability vector of dimension K. But still it's not clear what is a draw from a Dirichlet Process. What I understood is that a draw from a ...
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1answer
16 views

How can I show that my sample is random and a good representation of the population?

Okay, I'm looking at a population of user reviews. I have collected a random sample of the reviews and studied the trends of the words used and sentence structure. How do I make inferences about ...
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17 views

Performing a comparison between a sample distribution and population distribution in excel or nvivo

What is a relatively easy stats test to perform in excel/nvivo that is arguably reliable and valid and a good method for comparing a sample's normal distribution with a population's normal ...
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1answer
15 views

Running regressions on subsamples: Include the variable on which the subsample is based in the regressions?

Income is one of my independent variables in a sample of 2000 households. I'd like split the sample along household income lines (poor, vulnerable and non-poor). Is there a reason not to include ...
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1answer
88 views

Mutual Exclusivity

Suppose that a study is being done on all families with one, two, or three children. Let the outcomes of the study be the genders of the children in descending order of their age. A. List sample ...
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20 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 ...
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17 views

Minimum sample size in nonparametric data

My population has more or less 80,000 individuals and I would like to take a small sample with a high probability it is really close to the whole population. The problem is that my data is ...
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12 views

probability of sample proportion

I am trying to find the z-score for a sample proportion of 0.39 (The question is actually asking to find the probability of the sample proportion that is greater than .39). The only information ...
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3answers
40 views

Distribution of the average of a sample of standard deviations

I have a sample of standard deviations. How is its average distributed? The sample is not big so normality is hardly possible. A.B.
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1answer
41 views

Calculating sample size in R

I'm trying to calculate sample size and I have a Cohen F of .25, and I want to use power of .8. Is there a function in R that will let me calculate sample size based on these values? THANKS!!!!
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1answer
25 views

Deriving the formula for the mean of a stratified sample

The formula for the mean of a stratified sample $\bar Y_s$ is: $$\bar Y_s = \frac 1 N \sum_i N_i \bar Y_i$$ where $N$ is the sample size for all strata, and $N_i$ and $Y_i$ are the sample size and ...
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13 views

How to quantify the similarity between two samples using quartiles only?

I have several sets of samples I would like to compare. Each set is comprised of two samples, for which I only have the quartiles, min/max values and sample size for each sample. I would like to ...
2
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1answer
30 views

A non-i.i.d observations in a Bayesian inference problem

Suppose we have a simple Bayesian network which has two variables $x$ and $y$, $x$ is the parent of $y$. We sample $M$ $x$s independently based on $P(x)$, named $x_1,\ldots,x_M$, and for every $x_i$, ...
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0answers
283 views

Calculate at .05 level of significance

A research organization claims that the monthly wages of industrial workers in district X exceed those in district Y by more than Rs 150. Two different samples drawn independently from the two ...
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2answers
18 views

Large difference in number of cases in each category of a variable

I want to run an analysis on a data set. However, the primary predictor variable (5 point scale) varies greatly in size of each group. I plan to create a dichotomous variable from these 5 category. ...
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1answer
14 views

Advice on which test to run to show a valid sample of participants

I have collected data on medical diagnosis and am wanting to know which test I should use to show my participants are similar to a pre and post intervention. The first set of data yielded 53% male ...
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0answers
24 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 ...
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21 views

In search of a proper similarity function

I'm trying to find the most similar sample between a candidate and a bag of samples. Consider you have a knowledge corpus as follows: ...
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2answers
67 views

Alternative to z test for massive samples?

I'm trying to compare a number of large data sets (over 3000 samples per set), when I plot histograms of these distributions I can see two which are clearly different and a z-test confirms this, which ...
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2answers
45 views

How do you draw a random sample of unique IDs in a large dataset?

Rookie here -- I have a a large data set with about 75,000 observations, and 2000 unique IDs. Therefore, each unique ID has about 37 observations. I'm trying to draw a random sample of unique IDs, say ...
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2answers
205 views

Bootstrap: the issue of overfitting

Suppose one performs the so-called non-parametric bootstrap by drawing $B$ samples of size $n$ each from the original $n$ observations with replacement. I believe this procedure is equivalent to ...
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0answers
45 views

Should I use independent samples t-test?

I need to analyse if there's a difference between poor and rich European countries (using a GDP per capita index variable) and look if it has an effect on the variable environment. The GDP per capita ...
2
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1answer
91 views

Kolmogorov-Smirnov for Pareto distribution on sample

I want to use the Kolmogorov-Smirnov test to test if a sample is drawn from a Pareto distribution. Unfortunately, the only way to estimate the distribution's parameters is from the sample. Does ...
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1answer
41 views

Out-of-sample vs. test set

Someone asked me if I did out-of-time testing (which I assume is just out-of-sample testing but with a timeline element). But if I have a test set, is that not essentially the same as out-of-sample ...
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7 views

Select most different observations

I have a polar chart representing eight dimensional observations as 'rings' around the center. Furthermore, I am limited to Excel for graphing purposes, which means I can only display 255 series at ...
2
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0answers
40 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 ...
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57 views

Out-of-time testing (basic question)

I understand the importance of out-of-sample testing, but could you tell me why I should (or shouldn't) do out-of-time testing ? The only use that comes to mind is if the predictive model applies to ...
3
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1answer
76 views

wilson's adjustment for sample proportion

Could somebody provide a derivation for Wilson's adjustment for the CI of a sample proportion? The formula is: $$\tilde{p} \approx \frac{x+2}{n+4}$$ where $x$ is the number of successes, and $n$ is ...
2
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1answer
33 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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1answer
10 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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0answers
35 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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1answer
55 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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0answers
35 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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0answers
109 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
290 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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1answer
41 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 ...
0
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1answer
67 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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1answer
23 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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0answers
24 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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0answers
32 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
126 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
19 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 ...
2
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0answers
52 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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0answers
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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59 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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0answers
41 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 ...
2
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0answers
31 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 ...
2
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0answers
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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0answers
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? ...