Creating samples from a well-specified population using a probabilistic method and/or producing random numbers from a specified distribution.

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10 views

Optimally sampling a sequence of observations

Given a multivariate population, I'd like to define a sequence of observations to sample, such that coverage and representativeness is optimal at each step (cumulatively). For example, a sample of ...
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93 views

How to generate two groups of $n$ random numbers in $U(0,1)$ such that sum of these two groups equal? [on hold]

I want to have two groups of $n$ random numbers $u_i$ and $v_i$ in $U(0,1)$, such that $\sum u_i = \sum v_i$ What I tried is: I can firstly get $u_i$ by $U\sim U(0,1)$, make $s=\sum u_i$. Then I ...
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13 views

please I want to know what type of study its when certain variables are examined for in type 2 diabetics? [on hold]

I dont have a training in statistic. And am doing a research work on the effect of mean platelet volume and von willebrand factor in type 2 diabetics
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35 views

SEM with categorical complex survey data adjusting for cluster effect

My data comes from a two stage stratified cluster sample. There are some categorical (ordinal) manifest (dependent/endogenous) variables. I believe these variables can be divided into three major ...
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1answer
33 views

Random sampling from a population with mutually dependent elements

After reading this answer, I found myself confused. Say I am looking for the percentage of people who are likely to vote for a particular candidate. I am sampling from a population which is known to ...
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1answer
46 views

sampling distribution for N(0,1) samples

Here is an portion of my lecture notes from class, we are studying sampling distributions. I am confused on some of the examples that are showed in the attached picture. For the first example, ...
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12 views

Jittery sampling of jittery events - what to prioritize

Stat beginner with a practical problem. In an industrial application, I'm sampling a repetitive production process, to generate a histogram of the cycle time. The cycle time of course varies somewhat ...
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20 views

How to generate conditioned random variables from a density function?

I want to generate random variables from a distribution function using inverse sampling with the additional condition that the sampling should be conditioned, i.e., random generated variables should ...
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17 views

Two-stage sampling with R [on hold]

I have been trying to do a two-stage survey sampling using the mstage function. My sampling frame consists of 23 primary sampling units (...
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19 views

Relation between precision, recall and sample size

I have a large data set for binary classification problem. Now in order to fit model to data I have been trying modeling using various sample size. For each sample size I gets a different precision ...
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17 views

Combining two different sampling methods

Let's say I want to quantify the preference that people have towards shoe color as a function of their age. For simplicity, assume there are only black, gray, and brown shoes. First I ask 1,000 ...
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1answer
24 views

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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15 views

Combining results of two independent quantitative studies

I'm wondering if it is possible to combine the results of two independent surveys. Survey 1 is a nationwide study with a base of 1200, whereas , survey 2 is a survey of specific province only with a ...
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30 views

How large of a sample size is needed for non-experimental longitudinal data?

I am doing research on the causal effect of student jobs on later job prospects. I am ultimately going to use work employers responses as my input data (i.e. how they respond to CV's that either have ...
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15 views

What is the minimum of number of participants for a 2 by 2 by 2 design..? [closed]

I am collecting data for my dissertation. What is the minimum I need?thanks.
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30 views

how to measure the likelihood of a sample?

I am selecting a sample of features from a large pool with each feature having a different frequency and hence probability of being selected. The probability of selecting any given combination of ...
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61 views

Probability of failure in a finite population

I regularly inspect finite populations for failures (we make custom products in batches of ~500-1000). Currently, we inspect every product for failure, which is quite a bit of work. I want to reduce ...
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27 views

Sampling rate and regression

I am interested in developing a regression model. The data (about 1000 observations) that I have are not really random (i.e., spatially, the closest ones are correlated to some degree), so I drew a ...
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20 views

Exact Confidence Interval for Proportion Estimated with Cluster Sampling

Can anyone suggest a reference that discusses how to calculate an exact confidence interval (i.e., does not use the normal approximation) for a proportion estimated from a single stage cluster sample ...
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7 views

Cluster Component Coefficient Calculation for data in Rows

I have my data in the form such as: ...
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16 views

Software performace [migrated]

I have a software that I need to test for performance. I automated it but wanted to know how many times do I need to run it? It takes 20 mins to complete a full test and I have days if required.
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13 views

estimating time-varying likelyhood

I have a random variable that can have a binary outcome, with True having a likelihood p(t) with t meaning time. I need to estimate p(now). If p were constant I could increase the sample to get a more ...
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20 views

Sample size to calculate median average for large population

I have a large dataset of individual's forename and birth year. I'd like to know the average birth year of people with different forenames, or more specifically, how many name/year pairs do I need to ...
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1answer
82 views

Does this Monte Carlo Technique Have a Name?

I sketched this algorithm out the other night. I am sure it has a name, I just do not know what it is yet. It would be helpful if someone could point me in the right direction for research. I ...
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2answers
75 views

Sample from distribution given by histogram

Given a histogram obtained using given data points, how do I randomly sample from the distribution predicted by the histogram? Any conceptual comment / R code would be welcome.
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34 views

Relationship between CLT for estimator of sample and number of combinations for subsample?

What is the relationship between the Central Limit Theorem as applied to the expected value of an estimator of a parent sample and the number of possible combinations of a subsample used to calculate ...
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1answer
37 views

justification of Monte Carlo integration

I came across the following justification of Monte Carlo integration, where $p(x)=\frac{1}{b-a}$ $E[F_N]=E\bigg[ \frac{b-a}{N} \sum \limits_{i=1}^{N}f(X_i) \bigg]$ $= \frac{b-a}{N} \sum ...
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18 views

Sampling combinations

I'm running a simulation where the different inputs are combinations of $n$ values taken in $r$. The problem is that even though $n$ is small, the number of different combinations is very large, so I ...
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1answer
32 views

How to create a representative sample from a population of students?

I have a population around 300,000 students who are in around 1000 schools. Out of these 1000 schools there are 50 "special schools". All schools fall into 70 districts (which are themselves in 14 ...
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1answer
33 views

sock drawer problems and sampling without replacement

Could I get help on this "sampling without replacement" question please? In a drawer, there are 10 socks, six RED and four BLUE. Q1: If you were to get four socks in a row, what is the probability ...
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2answers
38 views

Variance calculation [duplicate]

Can someone explain why: Given a set of n independent observations Z1...Zn, each with variance K. The variance of the mean is K/n?
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17 views

Can I show that the “random user” feature of a website is fair?

I have a script selecting random users from deviantArt using their "Random user" feature. Is there a way to be confident that the users that they select are unbiased--that every user has an equal ...
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1answer
24 views

What are those variables in Cochran's formula

I cannot find any information about the Cochran's formula below: $$\text{Sample Size} = \frac{n}{1 + (n/\text{population})}$$ in which $n$ is equal to $Z * Z [P (1-P)/(D*D)]$ So I assume Z is the ...
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2answers
49 views

Difference in Group Sample Rate, not Size, based on Independent Variable

I'm working on a study that involves measuring breathing effort of an individual over short periods of time (specifically breath distention). The dependent variable is based on a new therapeutic and ...
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14 views

How to determine the proper sample size and testing criteria range for an experiment design?

I am currently trying to design an experiment that will be testing how fast a conveyor is able to convey different size cases. The case sizes are based on 4 dimensions (LxWxH and Weight) and the case ...
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1answer
32 views

Appropriate model for feature subset selection

I am working with a feature selection problem. What I am trying to do is find optimal subset of features for classification. My data consist of 100 features and 300 instances, and class label is ...
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1answer
34 views

When would you want to reduce variance?

In a sampling-estimation context, low variance of the estimate is a goal. Several things I've read suggest (though I can't quite connect the dots) that lowering variance in the data will improve the ...
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2answers
57 views

Sampling with Replacement Question

I was just stumped on a lottery themed question that seems like it should be easy...: In RI they do second chance drawings where you send in spent scratchers and they draw from all of the ones sent ...
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30 views

How to sample random variables (x,y) from a bivariate Cauchy distribution using a Gibbs sampler?

A bivariate Cauchy distribution is equivalent to a bivariate t-distribution with 1 degree of freedom.
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81 views

Error in the design of an experiment

Suppose that we have a population with a subpopulation that exhibits a certain characteristic. We are interested in the performance of a group of people from the population on a group test. The ...
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11 views

Generate samples from frequency table with fixed values [migrated]

I have a population 2x2 frequency table, with specific values: 20, 37, 37, 20. I need to generate N number of samples from this population (for simulation purposes). How can I do it in R?
3
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1answer
28 views

Producing samples from exponential family when sufficient statistics are known

Suppose I have a distribution which belongs to an exponential family, of the form $$p(x) = \frac{\exp(-\sum_k \eta_k T_k(x))}{Z},$$ where $T_k(x)$ are a fixed set of sufficient statistics, $\eta_k$ ...
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14 views

Mean and Variance of Aggregations with Uneven Sample Sizes

I am doing online aggregation of large datasets, as discussed in Hellerstein et al.. Short description: I have a multi-billion point dataset, and want to aggregate over certain dimensions. For ...
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1answer
660 views

Did I just invent a Bayesian method for analysis of ROC curves?

Preamble This is a long post. If you're re-reading this, please note that I've revised the question portion, though the background material remains the same. Additionally, I believe that I've devised ...
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53 views

Can survey sample sizes be used for quality control sampling? Is the formula that easy?

I have no solid background in statistics so please bear with me. In general, I am trying to figure out methods to determine sample sizes required to establish a certain level of confidence for a ...
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60 views

Determine required sample size with unknown standard deviation

An exercise : A quality control engineer gets 1000 items. How big a sample will he require to say that the he is 95% confident that the sample represents the population?? Is this possible to answer ...
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89 views

Offshore Wind Assessment

Does anyone know if Latin Hypercube sampling can be effective in the statistical analysis of offshore wind time series in order to reproduce random wind fields with a small amount of observed data? ...
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1answer
86 views

Confidence Levels for Mean of measured distribution

I have measured some values. These values are already aggregates (in principle average values). The values have a "non-nice" distribution, for example . They come from different sources with different ...
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22 views

I can sample 10% data at an intersection every day for 10 days. What should I use as n in calculating the Standard Error?

I am able to obtain 10% of vehicle travel time information at an intersection for 10 days at the same hour of the day. If we consider that the number of vehicles arriving at the intersection in all 10 ...
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19 views

Calculating the amount of underestimation

Coverage rate for a parameter is 91.2%, and the nominal coverage rate is 95%. If the confidence interval is based on asymptotic standard normal, then the amount of coverage 91.2% implies that the ...