Questions tagged [sample]

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.

Filter by
Sorted by
Tagged with
2
votes
1answer
26 views

Calculating sample size with standard deviation?

Okay so I have an exam coming up pretty soon and I really can't get the hang of how to calculate sample size when all you are given is standard deviation. For instance: A normal population has a ...
0
votes
0answers
6 views

Sample size for uniform multinomial to control minimum

I'm interested in controlling the minimum for a uniform multinomial distribution. Specifically, What would be the sample size to have the following inequality regarding the minimum? Do you know of ...
-2
votes
0answers
39 views

I Need Help!!! I can't understand this statistics homework! [closed]

In an election, suppose that 55% of voters support creating a new fire district. If we poll 163 of these voters at random, the probability distribution for the proportion of the polled voters that ...
1
vote
0answers
15 views

Is a non stratified survey sample 70,000 people sufficient to make conclusions about a population of 12 million people?

Is a survey with a sample size of 70,000 people sufficient to make conclusions about a population of 12 million people when there is no way to ensure that the sample is stratified sample where the ...
1
vote
1answer
23 views

Which statistical tests can I use to analyse significant difference between the means of non-random samples? [duplicate]

I want to compare the means of non-random samples to population mean. However, most standard tests (eg. t-tests, ANOVA, Welch test etc.) are based on the assumption that samples are randomly obtained ...
0
votes
1answer
39 views

unknown standard deviation = range/4

Suppose you want to estimate the average age of all Boeing 737-300 airplanes now in active domestic U.S. service. You want to be 95% confident, and you want your estimate to be within one year of the ...
0
votes
0answers
19 views

sigma is unknown, so it must be estimated by using sigma approximately equals (1/4) * (range) [duplicate]

Suppose you want to estimate the average age of all Boeing 737-300 airplanes now in active domestic U.S. service. You want to be 95% confident, and you want your estimate to be within one year of the ...
0
votes
0answers
13 views

Bayesian posterior guarantees [duplicate]

I have a quantity that I know before hand is a constant. The instrument used to measure this quantity creates measurements that are noisy with zero bias. Suppose the constant is $c$ then the ...
0
votes
1answer
22 views

How to derive p value of whether there exists a difference (given before and after correlation, averages, and standard deviations)?

I am trying to solve the following question: A chemical refining process is monitored before and after the plant is shut down and cleaned. At 40 randomly selected outputs, before cleaning, ...
1
vote
0answers
12 views

Representativeness of sample, distribution of age from sample compared to national sample

Please forgive my entry-level question. I have been slamming my head on the table for well over 3 hours now as I cannot seem to figure this one out. I have a sample of n=450, population is about 17m....
0
votes
0answers
10 views

split (or better full sample) dataframe with conditions

I'm pretty new to R and this kind of tasks, I'm deeply sorry if the question is not correct or malformed: I have some data in Excel, like the following: ...
2
votes
1answer
43 views

How to estimate log-normal distribution parameters from a set of data?

I don't have any background in statistics, so maybe I may say things that are incorrect. I have to model the production of waste deposition at each container of a set of containers and I have access ...
1
vote
0answers
9 views

Sample Variance Quandry [duplicate]

I was working on an explicit example for a student of mine, and I ran into a bump. Assume that the population is $\{1,2,4\}$. I draw samples of size 2 (without replacement) from the population. From ...
1
vote
0answers
33 views

how to infer population proportion from samples from 2 disjoint subgroups?

Suppose that I know that a large population consists of equal numbers of men and women. I sample 1000 men and ask whether they have ever eaten an avocado. Some number M say yes. Then I sample 1000 ...
0
votes
0answers
12 views

One Point Sample Size Information [duplicate]

Is there ever a 1 person sample size? Is there a 1 sample size for a computer program? When does a 1 data point sample size make sense?
4
votes
2answers
159 views

Sample Variance and Dividing by $n-1$

In this video... https://www.youtube.com/watch?v=sHRBg6BhKjI ...and in many others, the explanation for why when calculating the sample variance we divide by $n-1$ instead of by $n$ is the following:...
-1
votes
1answer
25 views

Can we tell anything at all about $ \frac {S_n^2}{\sigma^2} $ if we know that the distribution is normal?

Suppose we don't know anything about a distribution except that it is a Normal distribution with mean $ \mu $ and variance $ \sigma^2 $. Can we argue, theoretically, the sample variance, $ S_n^2 $ ...
1
vote
0answers
25 views

Determining Sample Size When Low Probability Items Are Of Interest [closed]

Let's assume there are 10,000,000 Yankee fans and we want to analyze what else these 10 million people are fans of. A simple question is, what sample size do we need to be confident in the results? ...
-1
votes
1answer
17 views

Rather use a sample of a population or analyze a whole population but smaller?

I am validating an automated surveillance program. It is about infection incidence on a hospital ward. I could easily check if the small list of infections produced by the automated surveillance ...
1
vote
1answer
32 views

How would I calculate the standard deviation of a sample given the sample size, mean, and sum of the data's squares?

For example, given: $\sum_{i=1}^n x_i^2 = 10$, $n=10$, and $mean = 10$, how would I go about calculating the standard deviation? The formula for standard deviation requires me knowing what $\sum_{i=1}^...
0
votes
0answers
17 views

Testing significance: single population, two-sample unpaired data

I am looking to test the significance of a training/ education program of home building construction. I am working with unpaired data of a dependent sample and am unsure how to proceed. Since the ...
3
votes
0answers
40 views

“Unselected sample” vs “random sample”

I've just encountered the term "unselected sample" for the first time, which seems to be fairly commonly used in medicine. Example usages: Climacteric symptoms in an unselected sample of Swedish ...
0
votes
0answers
26 views
0
votes
0answers
11 views

Is there a known connection between correction factors (from calibration) and standard error in estimation (in survey sampling)?

I have a response dataset that is very far from representative. The sample was drawn SRS. Some population groups are much more likely to respond than others, so calibration (to known population totals)...
0
votes
0answers
24 views

Truncation of distance matrix

Given a sample $\textbf{X}_1$,...,$\textbf{X}_n\in\mathbb{R}^p$ from an arbitrary distribution with distribution function $F$ we can calculate the pairwise Mahalanobis distances between the sample ...
0
votes
0answers
8 views

How to be confident in the specificity of a threshold?

I am a student in a hospital department and looking back through ~5 years of testing I have found ~70 patients who received a test. I found a threshold which is the lowest result compatible with ...
1
vote
1answer
40 views

Selecting a proper sample from a dataset for a hypothesis test

I have a dataset of about 800k subjects and within that dataset 7025 subjects have either disease A or disease B. I'd like to test the hypothesis (chi squared test) that subjects with disease A are ...
0
votes
2answers
46 views

Two-sample KS test results vs distributions

WARNING : MAJOR UPDATE BELOW, I've made a mistake I am currently working on validating a predictive model that was made some years ago. In doing so, I am comparing the distribution of the Target ...
2
votes
0answers
16 views

Expected standard deviation of probabilistic sample

Let's say I have a collection of $n$ individuals, each individual is associated with a single value $x_i$, with $i = 1, 2, 3, ... n$. I now gather a sample of $s$ individuals from this collection, ...
2
votes
1answer
58 views

Sample size and variance

A random sample of size n1 = 16 is selected from a normal population with a mean of 75 and a standard deviation of 8. A second random sample of size n2 = 9 is taken from another normal population with ...
1
vote
0answers
46 views

Is the difference between two samples of two distributions a sample of the difference of the distributions? [closed]

My question is as follows. Suppose you have two variables $X$, $Y$. If I pick a random sample $x$ from the distribution over $X$ that has probability density function $f_X$, and another random sample $...
2
votes
1answer
54 views

Distribution of the sample variance $S^2$ from a normal population [closed]

Let $X_1, X_2, X_3, ….., X_n$ be $N(\mu, \sigma^2)$ distributed. Then what is the distribution of $S^2$ I have already proven that if $X_i$ are $N(\mu, \sigma^2)$, then $\frac{(n-1)S^2}{\sigma^2}$ ...
1
vote
0answers
54 views

Weird sample variance when creating a lognromal sample with pre-defined mean and variance [duplicate]

I have been working with lognormal distributions as a proposal distribution for some MCMC routines which require the proposal distribution to have some pre-defined sample mean and variance, $m$ and $v$...
2
votes
1answer
34 views

Is this a valid way to get a simple random sample?

I have a data set of about 200,000 observations about establishments in my district and their operating time. I need to establish the correctness of my data. Consequently, I am trying to take a simple ...
0
votes
0answers
34 views

Probability and Normal Distribution

(sampling distribution) We randomly draw another sample of size $10$. What is the probability that the mean word count of these $10$ songs is greater than $436.531 = 374.9149 + \dfrac{2∗97.42498}{\...
0
votes
1answer
23 views

Probability of several consecutive drawn random samples of a standard normal distribution exceeding a certain value [closed]

I have trouble figuring out the following: I have a standard normal distribution (µ = 0, σ² = 1) and now draw n random independent samples. Lets assume the following: n = 3 What is the chance, that ...
1
vote
1answer
17 views

Logit regression (Panel data): resample?

I have a panel data (all listed companies in the US with quarterly data) in which the dependent variable is 1 if the company was recommended on a investment recommendations website, and 0 otherwise. ...
1
vote
1answer
27 views

Choosing the correct hypotheses [closed]

I was trying out some questions on hypothesis testing when some questions started challenging me. Here is an example: A lot of product X is to be rejected if the temperature of the lot is greater ...
2
votes
1answer
69 views

Determine sample size using reversed goodness of fit

I am asked to work on a specific problem in which I have to calculate certain expenditures for an industry, consisting of a population of about 400 companies. Although I already suggested to conduct a ...
0
votes
1answer
26 views

Proof that covariance of RV and group average is less than variance of RV

I have a random variable $X_i$ and a group of $N_j$ other random variables that includes $X_i$. Let's just call this group $J$. There are no distributional assumptions made on these RVs (other than ...
0
votes
0answers
33 views

Different sample size of control and test groups

Hope someone can help my question: I have a survey study with one control group and one test group. Each is set to have 500 completes. However, we are short in sample in one group: Test is 350 and ...
0
votes
1answer
44 views

Infering population from a sample?

I took a test in class and found it to be difficult. So I asked in my WhatsApp group if others felt the same. 4/36 people replied yes they felt it difficult. Others did not respond either in yes or no....
0
votes
1answer
18 views

How to calculate the Margin of Error in this specific scenario?

Assuming I have a population made of hotel bookings for a specific period and I need to send a survey questionnaire to each guest (guest=booking) by email. To simplify things, let us assume the ...
0
votes
0answers
33 views

Confidence Interval for the Difference Between Proportions in complex samples

I have two complex samples (with different sizes) from the same population in different times. I used the survey package to create designs for them: ...
1
vote
1answer
109 views

Calculate a Conditional Expectation via Samples

Consider a binary random variable $Y \sim p(Y)$, a random variable $X \sim p(X)$ (can be discrete or continuous) and a conditional distribution $p(X|Y)$. Suppose that I generate $N$ samples from $p(Y)$...
2
votes
1answer
124 views

intuition behind SD+

so i was reading statistics by Freedman and in the section where he describes the t-test he goes on to explain why we would use the SD+ instead of the regular SD to calculate the S.E with the sample ...
2
votes
1answer
29 views

How do I sample N items from a list ensuring the samples are as similar as possible to each other?

Is there anyway to sample 6 numbers without replacement this list of 12 numbers ...
0
votes
0answers
46 views

2x3 design, binary out come sample size calculation?

I'm designing an experiment as part of a marketing assignment. I'm planning on running a 2*3 between-subjects design (6 conditions comprised of two factors, one with 2 levels and one with 3 levels). ...
0
votes
1answer
41 views

How can we write the sample variance's formal definition of a continuous random variable considering Bessel's correction? [closed]

I am trying to find the formal way of writing the sample variance of a continuous random variable considering Bessel's correction. I ask because the sample variance is usually written this way: $$ ...
0
votes
0answers
20 views

When to use a certain sampling technique

I'm taking a class where we learn about different sampling techniques. For the most part it has come down to SRS, Ratio/Regression/Difference estimation, Stratified random sampling, Systematic ...