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.
2
votes
1answer
31 views
How to standardise cases within groups to perform ranking across groups and over time?
I am trying to create a method to rank ships according to their fuel burn rates. There are two different classes of ships, with different burn rates, so I am trying to create a mean and standard ...
4
votes
1answer
28 views
Population standard deviation for a binomial(?) distribution?
I have been confused by two separate questions (Stock & Watson - introduction to econometrics ch.3), using different values for standard errors.
The first: In a survey of 400 voters, 215 respond ...
0
votes
0answers
17 views
Combining covariances
Imagine we have one sample (n=40) from a population on 2 variables, for which we estimate the covariance (say, 0.1). If we would have another sample (n=10) from the same population, and we estimate ...
5
votes
0answers
68 views
Large sample asymptotic/theory - Why to care about?
I hope that this question does not get marked "as too general" and hope a discussion gets started that benefits all.
In statistics, we spend a lot of time learning large sample theories. We are ...
0
votes
0answers
18 views
Constructing a sample
I have a vector of 0's and 1's from a finite population, where there is an unequal proportion of 0's and 1's. How can I construct a sample (with replacement) from this population with an equal number ...
0
votes
0answers
14 views
What test to asses the complication a treatment has with a small sample size(80) and only 5-10% complication rate?
I am assessing the benefit of using a therapeutic intervention in a population of 80 people split evenly into two groups. The benefit is to decrease a certain complication which only has a incidence ...
1
vote
2answers
49 views
Relationships between the corr(x,y) and corr(x,y) on a subset
Suppose two sets of data $\mathbf{X}$ and $\mathbf{Y}$ have a correlation of $\rho_0$. Can anything be said about the correlation between $\mathbf{X}_1$ and $\mathbf{Y}_1$ and $\mathbf{X}_2$ and ...
2
votes
0answers
39 views
What do people call the groups into which quantiles divide the population?
Is there a correct technical name for the group of observations between two quantiles? For example, if you have the values of the four cut-points that divide a population into five groups of equal ...
0
votes
0answers
17 views
Tolerance as the probability of success
Often you try to find the number of samples needed (at least a lower bound) to meet a certain level of tolerance $ε$ that is usually given as some sort of absolute value. Generally done like so:
• $n ...
0
votes
0answers
42 views
Determining sample size in a non-normaly distributed data
I want to take some samples from a database nearly ~150.000 records of a non-normally distributed values. From this link I obtained some common procedures to find a sample, influenced by The level of ...
0
votes
0answers
39 views
What is the minimum sample size for discrete choice experiment (DCE)?
I am preparing to conduct a DCE and am unsure on the sample size that will lead to significant results. I will have 3 alternatives with 5 attributes for each. Some will be generic while some will be ...
0
votes
1answer
103 views
Regression on means of log-transformed variables
Suppose that I want to study the relationship between two variables $Y$ and $X$ using the linear model $Y \sim X$. Unfortunately, both $Y$ and $X$ are not normally distributed, say they are both ...
0
votes
1answer
46 views
Alternatives to svychisq() in survey
A time ago I posted this question. Now I have a 'little' continuation: I'm having some difficult with a few questions, getting this error message:
...
0
votes
0answers
28 views
Replicates in logistic regression: identifying significant factors
I'm investigating whether the factors Height (3 levels) and Distance (3 levels) have a significant effect on the proportion of females that are mated by males radiating from a central source. My ...
5
votes
1answer
73 views
Consistency of sample quantile
I'm new to statistics and recently I learnt about non-parametric estimation. On the estimation of empirical quantiles, many notes talk about the asymptotic behavior of sample quantiles. The proof is ...
1
vote
1answer
67 views
Analysis of complex sample
The company where I work did a survey with a complex sample. Originally, the sample was a 2-step stratified, but due to some problems, we lost one of them (so, let's consider that the sample is ...
1
vote
1answer
14 views
Unbiased estimator from two SRS less duplicates
Suppose I take two independent random samples from a population of size $N$: the first is a simple random sample of size $n$ and the second is a simple random sample of size $m$. Let set $S$ contain ...
0
votes
1answer
86 views
How can I find the standard deviation in categorical distribution
How can I find the standard deviation in categorical distribution, where the elements have non-numerical attributes (e.g. colors)?
For example, I have a bag of marbles with $n$ colors. There's an ...
1
vote
2answers
99 views
Population Variance and Sample Variance
How is it that lowering the number of frequence,$n$ by $1$ in the for formula for Population and Sample Variance account for the discrepency of using sample rather than population.
I mean how is ...
0
votes
0answers
63 views
Prove one assumption in confidence interval for difference in means
How to prove that
$\sqrt{( s_1^2 / n_1 + s_2^2 / n_2)}$ converge in probability to $\sqrt{( \sigma_1^2 / n_1 + \sigma_2^2 / n_2)}$?
$s^2$ converge in probability to $\sigma^2$, when n goes to ...
4
votes
2answers
73 views
Definition of a sample: can it include the same object twice?
Wikipedia defines a sample as:
a subset of a population.
While exploring the reason why we divide by $(n-1)$ instead of $n$ when calculating standard deviation (discussed in this question), I ...
3
votes
1answer
99 views
Estimating parameters of a normal distribution from noisy observation of samples
Suppose I have a number of samples drawn from a normal distribution $x_i \sim \mathcal{N}(\mu,C)$ with $i = 1 \dots n$. I can make observations $z_i = x_i + e_i$ for those samples which are perturbed ...
0
votes
0answers
29 views
audit sample prediction
I have a finite population of transaction data. The data is broken down into various sub-categories.
A subset of these transactions has been audited and determined to either pass or fail.
I want to ...
3
votes
0answers
50 views
Bounds for the population variance?
Suppose we have i.i.d. samples $x_1$, $\ldots$, $x_n$ for a (potentially non-normal) random variable $X$ with finite moments. We can use these samples to construct an unbiased estimates of the ...
2
votes
1answer
113 views
Expectation of the sample median for symmetric distributions
Is the sample median an unbiased estimator of the population mean when the distribution is symmetric?
7
votes
5answers
364 views
If not a Poisson, then what distribution is this?
I have a data set containing the number of actions performed by individuals over the course of 7 days. The specific action shouldn't be relevant for this question. Here are some descriptive statistics ...
0
votes
1answer
77 views
Population vs sample variance
This is perhaps a very basic question, but I am a bit confused. I have a time series of day some time varying data, say the amount of sunlight as the day passes.
I bucket the data in say 10 bins say ...
0
votes
1answer
108 views
Sample Standard Deviation - Did my teacher make a mistake (hypothesis testing)?
I first posted this one MSE, but it was pointed out to me that this site might be more suited for these types of questions (which is probably why this question wasn't answered for about 11 hours) over ...
1
vote
2answers
120 views
What's the bar above x called in the sample mean?
What's the bar above x called in the sample mean? Is it a diacritic mark?
0
votes
0answers
71 views
Minimum sample size
Probably a basic question, but here goes:
Suppose we have 1000 people who respond to a survey (500 men, 500 women)
Respondents can choose to "like" a series of pages.
Each respondent can "like" as ...
0
votes
0answers
69 views
Maximum of sample variance
Let $X_1, \dots, X_n$ be i.i.d from the interval $[0,1]$.
I am interested in situation when the sample variance
$$\frac{1}{n-1} \sum_{i=1}^n (X_i - \overline{X})^2$$ (where $\overline{X}$ is sample ...
0
votes
1answer
54 views
Factorial experiment with non-random sample – is it possible?
Factorial experiments have several advantages when one wants to examine the effect of several independent variables (factors) on an outcome. Perhaps most importantly, they often allow additional ...
2
votes
2answers
117 views
Testing null hypothesis with dependent samples
Let's say I conduct a survey of randomly selected 100 people, asking each of them two questions:
"Do you like NY?"
"Do you like LA?".
All 100 people responded. Among them, 60 answered "yes" about ...
0
votes
1answer
63 views
Identifying populations and samples from a dataset
I'm writing a proposal for a restrospective cohort study using registry data. Am I right to think of the registry data as the whole population?
If it is the population, then am I right in thinking ...
-1
votes
1answer
49 views
What kind of sample is this?
I took a sample from the university, but I stipulated that the sample students have to be at a specific mental age: 19 at the first year. The number of all students at the 1 year is known, but the ...
1
vote
0answers
172 views
What is the minimum sample size for discrete choice experiment?
I was wondering if there is a minimum sample size for conducting discrete choice experiment. From what I know, if choosing the number of sample size is a problem, one can resort to using the magic ...
4
votes
1answer
102 views
Multi-stage sampling together with hierarchical/ mixed effects models: which R packages?
Analyzing educational datasets we have samples of children from samples of class in samples of schools - we have sampling weights, so I use the survey package e.g. to do a linear model. But this kind ...
3
votes
0answers
94 views
Small n: non-parametric of parametric tests?
I am in a situation where I have sample with $n=19$, and the the data are not normally distributed (according to the results of a Kolmogorov-Smirnov test) for all the variables. The data were ...
0
votes
1answer
77 views
How to compute sample variance?
Suppose we have a sample of size n= 9, where the sum equals 27, and the sum of the squaredvalues equals 113. Sample mean is 27/9=3 and mean of squared values is 113/9 = 12.56 Can we then say that the ...
0
votes
0answers
16 views
Estimating the randomness of an SRS
I have noticed that normal population parameters can be estimated accurately with a reasonably small sample.
It occurs to me that this is only possible because of the assumption that the random ...
3
votes
0answers
45 views
How to calculate the 'loss' in information when decreasing sample size?
I have a questionnaire with ~40 questions where the respondent answers on a scale 1-7 on each question. At the moment we have a sample size of say 10,000 people.
The question is how I calculate the ...
0
votes
0answers
34 views
Very easy question : Sample Variance [duplicate]
Possible Duplicate:
How does the standard error work?
Let's say I have an unbiased estimator, which is the sample mean, to estimate $\theta$. When can you say that $$VAR[\overline{X}] = ...
1
vote
0answers
21 views
Sample/Filter nonuniformly distributed values so that result follows a uniform distribution
I have a dataset with a nonuniform distribution. I want to sample it so that the result is uniformly distributed. If I know the class of the example, with what probability should I choose it to get a ...
1
vote
1answer
62 views
Understanding random samples
I was looking at the following statement and felt I needed some help in sorting it out:
A random sample of size n from a population $f(x)$ is a collection of n independent random variables ...
1
vote
0answers
58 views
Independence of a single sample? [closed]
Is it possible to speak of the independence of a single sample (of multiple data points) relative to the underlying distribution? Or is independence only relevant between samples?
4
votes
3answers
117 views
Confusion between sample and population
A team has conducted a study in which an introductory class was
randomly divided into two groups. Group 1 was administered a dosage of
alcohol. Group 2 was given an equvialent dosage of ...
0
votes
4answers
262 views
Repeated coin flip experiments: what counts as a sample?
Apologies if this is a little confusing. If anything needs clarifying, I'll edit the question as best I can. Thanks.
If we take a sample of, say, 100 people, we could measure their heights, and ...
0
votes
0answers
148 views
What is minimum sample size to get significant?
I want to test whether there are any significant differences between Public Relation Strategies of the companies listed in the Malaysia Stock Exchange.
The total population is 825 companies within 13 ...
0
votes
0answers
56 views
Survey Weighted Regression Without FPC in R
I'm using the svydesign package in R to run survey weighted logit regressions as follows:
...
2
votes
2answers
2k views
Deciding whether to use r^2 or adjusted r^2 (specific situation)
I read online that it is only necessary to use adjusted-$R^2$ when you are working with a sample rather than the entire population.
The data I'm working with is information on a series of live ...
