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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1answer
15 views

Statistics - (bivariate data) Planning an Inquiry

I have to conduct a statistical inquiry that is representative of a population. You have to choose from a list of situations, and my choice was to measure the weight and length of carrots. The ...
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0answers
28 views

How to use/interpret bootstrapping?

I am working on an stochastic optimization problem. Now I have come across the idea of using Monte Carlo sampling approach to solve it. I need the empirical distribution or the true distribution of ...
1
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1answer
32 views

How to calculate sample size for this study design?

I am trying to find out whether the number of participants I recruited (N=42) so far is sufficient for my study in which: there are two interfaces (say A and B). ALL students in the study will try the ...
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0answers
7 views

Prior Probabilities vs Sampling

In case i have a dataset which has 100000 records and only 10000 of them represent Churn cases. Hence before building a predictive model i set a prior probability as 10% for CHURN and 90% for NON ...
2
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1answer
45 views

Number of different combinations in a sample

I hail from Mathematica SE. A friend of mine asked me a statistics question (I'm an economist and am assumed to know such things) which kind of stumped me, since I usually deal with non-discrete ...
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0answers
7 views

How to report sample size of an experimental study in a thesis based on power analysis?

I am not sure whether I have reported the sample size properly in my thesis which I have calculated based on power analysis. Please a have look: Based on a power analysis, the desired sample size ...
1
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1answer
180 views

Why doesn't the standard deviation represent a normal distribution?

Why doesn't the standard deviation of a sufficiently large sample represent a normal distribution that we can make inferences from? Let me list my thought process, so hopefully someone can highlight ...
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0answers
16 views

sample size power calculation

This is probably very simple but I am struggling...in a population there is a disease present clinically in around 35% of patients, we want to use two tests which when used in parallel have a ...
1
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1answer
38 views

Cohen's d in proportion test

I am calculating the sample size for proportion test. I would like to have significance level =0.05, power = 0.90 and that the effect size is greater that 5%. I would like to have statistically ...
0
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1answer
36 views

Sample size problem

I am looking for a suggestions on how to estimate the sample size in such a problem. There is a group with one usefull treatment (let's say 10 milion people) but one consider if there might be more ...
3
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2answers
73 views

Distribution of distributions

Could anybody point me towards material for dealing with data when your sample points are distributions in themselves? To be more specific each data point I am sampling has a mean and a variance, so I ...
0
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1answer
31 views

The difference between the standard error of the sample and the standard error of the mean value

I have an assignment that gives 48 counts of the same phenomena occurring over the same time interval. I am asked to a) Calculate the mean of the counts b) Calculate the standard error of the sample ...
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0answers
18 views

How do I count / display the number of each outcome from a random sample? [migrated]

I'm taking a sample of size 1000 of different (pet) animals. My code is pet <- sample(c("dog","cat","hamster","goldfish"), 1000, replace = TRUE) I want to ...
0
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1answer
36 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 ...
0
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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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0answers
18 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 ...
0
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1answer
20 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 ...
1
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1answer
94 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 ...
2
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0answers
21 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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0answers
18 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 ...
0
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0answers
13 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
43 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
45 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!!!!
1
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1answer
28 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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0answers
16 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
31 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
343 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. ...
0
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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 ...
2
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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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0answers
22 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
68 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
51 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 ...
9
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2answers
217 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
46 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
votes
1answer
100 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 ...
1
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1answer
53 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 ...
1
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0answers
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
42 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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0answers
85 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
196 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
34 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 ...
0
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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
40 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 ...
1
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1answer
65 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
36 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: ...
0
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0answers
150 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 ...
2
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3answers
302 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
44 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 ...