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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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
18 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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8 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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11 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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42 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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57 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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82 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 ...
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2answers
62 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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42 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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116 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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16 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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33 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?
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1answer
33 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
70 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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13 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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44 views

Heterogenous vs. homogeneous sample frame

1) I am interested to know why a homogeneous sample is required while recruiting subjects for a study, that will involve ANOVA and Regression Analysis. Is it not true that if the sample frame is ...
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13 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 ...
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1answer
35 views

Is my data representative of Bristol?

I've got some data about people in Bristol. I have about 75,000 records. Part of my dataset is each respondants age. Aside from this, I have also downloaded census data for Bristol, which gives me ...
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262 views

When is a sample proportion p hat instead of x bar

I just started my first statistics class and am not majoring in statistics so sorry if this sounds like a beginner question and also sorry if my language is incorrect. (feel free to correct me.) I ...
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38 views

Calculating the variance of sample mean?

I am working on time series analysis. The book I am using ("Statistics for Long Memory Processes" by Jan Beran) uses a number of measures for process memory and one of them is to graph Sample Mean ...
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42 views

Joint distribution of two related sample variances

Consider three time series x, v, w The distribution of the values that x,v,w take are zero-mean Gaussian, stationary and independent of time (no temporal colleration) and of each other. We know the ...
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61 views

Why do some researchers test for normality of sample data?

I once was a research assistant for a professor who wanted me to do some regressions, but before that he wanted me to test all the sample data for the variables to ensure they were normally ...
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2answers
47 views

What to do if samples aren't comparable?

I have an unbalanced panel data set, which covers a set of about 10 variables I am very interested in as controls in a regression. However, only a few of these variables are available in all waves: ...
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109 views

Prove that distribution of sample median (for even sample) is symmetric

Let $\mathbf{X}=(X_1,X_2,\ldots,X_{2k})$ be a sample from normal distribution $\mathcal{N}(0,1)$. Prove that distribution of sample median (for even sample) is symmetric around 0. $me(\mathbf{X}) = ...
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132 views

Which Distribution Does the Data Point Belong to?

I have two distributions which are derived from 2 separate sets of data. These distributions are not normal, and it is not clear at this point if they belong to any family of known pdfs (they are not ...
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30 views

Posterior distribution for true population variance

I have a process which may be assumed Gaussian - for now I'm assuming it to be zero-mean. The variance is unknown. I will estimate variance in the usual unbiased way to give the sample variance and ...
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78 views

Compare maxima of two Gaussian samples

Suppose $X$ and $Y$ are both normally distributed, with $X \sim \mathcal{N}(0,1)$ and $Y \sim \mathcal{N}(c,1),$ where $c > 0$. Consider $n$ independent draws of both $X$ and $Y$. As $n \rightarrow ...
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18 views

Appropriate bounding boxes on images for training data?

This is the first time I'm doing research in computer vision, and I'm going to be using OpenCV's cascaded training, for which I'm preparing positive samples for training data. If anyone's experienced ...
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1answer
53 views

Algorithm to take samples from binomial data

I am faced with the following problem : I have binomial data, ie. data of the form trials/successes, with a list of features. What I need is to sample without replacement from that data, ie. take a ...
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264 views

Does SurveyMonkey ignore the fact that you get a non-random sample?

SurveyMonkey has steps and a chart for you to figure out what sample size you need for a given margin of error or confidence interval, based on your population size. SurveyMonkey sample size Does ...
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29 views

Calculations using data captured over time seems to need a more advanced analysis method

I got a couple comments on my question. First of all, thank you very much. I was asked to be more clear. So, here's an attempt at that. I'm capturing raw data of play performance for each player ...
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64 views

Variance of a sum of functions of random variable

I'm trying to prove $$ \mathrm{Var}\left(\sum\limits_{i=1}^n{g(X_i)}\right) = n(Var(g(X_1))) $$ where $X_1...X_n$ are IID variables. I have been trying to use proof for a similar question - ...
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89 views

Sample Range to Estimate StDev

Accidentally, I found (by simulation) that the range of a normally distributed sample is related to the estimator of the standard deviation: $$X \sim \mathcal{N}\left(\mu, \sigma\right)$$ $$s(X) = ...
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1answer
96 views

Sample size calculation for a single proportion Without Any Comparisons (descriptive only): How to determine the margin of error in the formula?

I want to calculate the sample size for a single proportion (the prevalence of a disease). I know the formula and all: n = (z/m)^2 * P(1-P), where z is 1.96 (for 95% confidence level) and P stands for ...
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1answer
102 views

How to compare sampled areas to the Census?

I would like to discriminate sampled areas that are representative or not representative of their corresponding population, for a given characteristic. Suppose I have surveyed areas (i.e. Census ...
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1answer
127 views

Sample size calculation for comparison of 3 proportions

How do I calculate sample size for estimating difference in proportions between 3 groups? Most of the free sample size calculators have options for only 2 groups.
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50 views

Multilevel model and sample size

I want to estimate a complex hierarchical multilevel logit model with spatial structure. The model is a two-level-model. I have 20 regions (upper Level) which contain several districts (lower Level). ...
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60 views

Testing to see if a population is normal?

I'm an amateur statistician. I do it mostly for fun. I'm finishing up on my first semester stats class that covers up to hypothesis testing. I'm planning on beginning learning simple regression ...
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35 views

Representative sample or not?

Please help me out to determine of those are representative samples, not, or either: First example: A conservative talk radio host conducts a poll among his listeners. He asks his listeners to ...
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47 views

How do I address a known bias in my sample?

I have a population of interest ($N = 5000$) for which I know some demographic information. I have a sample 1500 members of that population. So I have a good sized sample, and I know exactly how it ...
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26 views

independent or dependent

I have situation in which I query different sites on the genome (biologically independent) and for each site I get a measurement. I have a number of measurements that are close together on the genome ...
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96 views

Alternatives to Horvitz–Thompson estimator

I am trying to estimate a mean of a population in a sample = ${\{x_1,..,x_n\}}$. I currently use 2 estimators: Sample mean = $\frac{\sum {x_i}}{n} $ Horvitz–Thompson estimator (HT) = $\frac{\sum ...
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1answer
75 views

Why describe a sample as i.i.d.?

I’m hoping for some help understanding the concept of RVs with respect to their use in the theory of drawing inferences on a population from a sample. To draw inferences on a population using a ...
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36 views

Using inferential statistics with groups that are unequal in size

I do clinical research and I am often asked to compare groups of vastly different group sizes. I try and get my clinicians to collapse categories when possible. I would like to definitively say that ...
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52 views

Need to verify sample is representative of known population of animals

I'm a biologist trying to verify that the age, gender, and family group of my samples from a population of whales is representative of the population, in order to make inferences in the discussion. ...
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55 views

Power Analysis and effect size

Appology if it is rather long. But i'm confused! What assumptions do i need in order to answer this question? With having two segments in the population that you wish to compare with respect to their ...
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1answer
87 views

Advantages of bootstrap aggregating (sampling)?

I am testing the robustness of a predictive model that I have previously established. I used to withdraw multiple random samples to see how robust the model is. Few days ago I came across bootstrap ...
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3answers
225 views

How to divide feature set for selection and training

I have training data with 260 observations that have a total of 7 classes. Each observation has 120 features. I applied feature selection based on the Bhattacharyya Algorithm and got the top 40 ...