# Tagged Questions

12 views

### Variance of total group based on variance and mean of subset

I came across dataset where they give annual mean and variance of a traitvalue, However, only for those individuals with positive traitvalue, all others have traitvalue = 0. I know the number of ...
124 views

### Is it possible to combine the F-test and t-test to test for differences in both the variance and the mean?

I would like to test $H_{0} :$ $\mu_{1} = \mu_{2}, \ \sigma_{1}^{2} = \sigma_{2}^{2}$ vs $H_{0} :$ $\mu_{1} \neq \mu_{2}, \ \sigma_{1}^{2} \neq \sigma_{2}^{2}$Is there a test statistic that would ...
70 views

### Finding the mean of a Gaussian distributed random variable given the variance

I have a Gaussian distributed random variable $X$ with known variance $\sigma^2$. Given that I know $P(X\geq t)=m$, how can I find the mean of the random variable?
29 views

### determining probability of spatial pattern metric greater than some instance

Let's say I have a grid of cells from a satellite image that take on the value of 0 or 1, with 1 being forest. There are many spatial pattern metrics that measure things about this pattern such as ...
55 views

### how to Normalize data(with noise) into 0-1 range good scale in mean and variance?

i have a matrix data. Perhaps some data in one cluster and another in some cluster. data scale is between [0-1000](just example). and i want to normalize into [0-1] and good in mean and variance. it ...
76 views

### how many years will it take to achieve six-sigma quality?

Suppose a business is operating at the three-sigma quality level. If projects have an average improvement rate of 50% annually, how many years will it take to achieve six-sigma quality?
40 views

### Updating variance of a dataset

In an application, I deal will a large number of images from which I successively extract particular values to compute their means and variances. Because storing them all would mean storing Gigas, I'd ...
166 views

### When does a distribution not have a mean or a variance?

I believe I read today a phrase which went something like this: If a distribution has a mean and a variance ... So I guess that means some distributions do not have means or variances? I fiend ...
27 views

### Is the square of coefficient of variation an ascending function of exponent c? [duplicate]

Suppose that $x$ is a random variable with any distribution that takes only positive values. If $z=x+1$, can the following inequality hold for constants $c_2>c_1>0$? ...
136 views

### Question about squares of the coefficients of variation

Suppose that $X$ is a random variable with any distribution that takes only positive values. Can the following inequality hold for constants $c_2 >c_1 >0$? ...
69 views

### Constrained mean variance optimization

I have some numbers $X={x_1,x_2,...,x_n}$. I add some small numbers to them and get $Y={y_1,y_2,...,y_n}$ where $y_i=x_i+\epsilon_i$. How can I find $Z={z_1,z_2,...,z_n}$ to minimize ...
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### ANOVA as Comparision of Means and Regression [duplicate]

ANOVA, ANalysis Of VAriance, is a method to compare means of several variables. At the same time it falls under G(eneral)LM in a sense that it a method for regression and used for regressing ...
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### How to test whether mean and variance is the same in two small samples?

I would like to test two relatively small samples against the null hypothesis that both their means and variances are the same. The alternative would be that they in fact differ. I saw a post on this ...
77 views

### Mean and variance of call center data

I have a fairly involved homework question, I was wondering if I could get some help. There are two types of phone calls arriving at a switch, long-duration and short-duration. Each day the number ...
43 views

### Mean and variance of number of tries required

So the question states that I'm trying something with an 85% chance of success, if I don't succeed I try again until I do. What is the mean and variance of the number of tries necessary until I ...
80 views

### Simple homework question about normally distributed variables

The question states: Consider a set of random variables $X_i$, where $i=1,...n$. Each $X_i$ is normally distributed with mean $0$ and variance $1$, i.e. $X_i$ are $\mathcal N(0,1)$. What is ...
24 views

### Variance of an estimator, as mean of $5$ estimates

Might be a stupid questions, but I realized it is something I haven't encountered until now. So I have 5 estimators for the same quantity, say $X_1,\dots, X_5$, (where each one uses a perturbed data ...
139 views

### Show that $E(XY) = σ_{XY} + μ_Xμ_Y$?

Let X and Y be two random variables with means $μ_X$ and $μ_Y$ , variances $σ^2_Y$, $σ^2_X$ and covariance $σ_{XY}$ . Show that $E(XY) = σ_{XY} + μ_Xμ_Y$? I tried the Covariance formula with: ...
338 views

### How can I find distribution from mean and variance

If I know the mean and variance of a discrete random variable $\in \{0,1,\dots \}$, How can I find the distribution?
90 views

### What is a (rule of thumb) good signal-to-noise ratio?

Is there a rule of thumb for a signal-to-noise ratio that can be considered "good"? In my case, for example, I got a signal-to-noise of 2.5, but in absence of a good benchmark I can't tell if this ...
47 views

### Calculate proportion among means with variance and CI

I have two groups of samples, with their own mean, SEM, CI. I would like to calculate the proportion in percentage between the two. Rationing the means is easy but I don't know very well I should I ...
59 views

### Compare variability in different groups

I have 3 groups with a distribution of samples. I used ANOVA to compare means of these groups and also fetched mean, SD and SEM. I have SD and SEM that varies among groups. How can I compare them so ...
95 views

### How large a variance can be for a discrete random variable whose mean is known?

In following Maximum value of coefficient of variation for bounded data set I come up this question: e.g., Say, $X$ can take integer values from $[0, 20]$ The mean of $X$ is known to be $0.005$ What ...
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### Statistical tests affected by the mean values of the two samples

The experiment consisted of this : 31 devices of type $A$ 26 devices of type $B$ All the 57 devices were side by side in order to measure the level of ambiant radiation. So, I have the doses for ...
132 views

### Find the mean and variance of $U_1 + U_2$

Let $Y_1, Y_2, Y_3$ be i.i.d continuous random variables. For $i = 1, 2$ define $U_i$ as $U_i=1$ if $Y_{i+1} > Y_i,$ $=0$ ,otherwise Find the mean and variance of $U_1 + U_2$ I can't find the ...
2k views

### Kurtosis/4th central moment in terms of mean and variance

Is it possible to express the kurtosis $\kappa$, or the 4th central moment $\mu_4$, of a random variable $X$ in terms of its mean $\mu = E(X)$ and variance $\sigma^2 = Var(X)$ only, without having to ...
831 views

### How to assess accuracy of phone GPS in measuring distances?

I am a complete stranger to statistics (apart from mandatory courses in college), but lately I ran into an interesting real-world scenario. Recently I started jogging. I take my GPS phone with me to ...
497 views

### How to combine subsets consisting of mean, variance, confidence, and number of sampled points used?

I have a data set that has been divided into $n$ data subsets. I am sampling from each of these subsets and getting a tuple consisting of mean, variance, confidence and number of sampled points used. ...
305 views

### R limma voom function mean-variance trend

I am using the limma package in R to do some analysis on a count data matrix. I use the voom function and that normally creates a plot with the mean variance trend line in it. Now I created also a ...
1k views

### What does a squared coefficient of variation signify?

The coefficient of variation is defined as the ratio of S.D to mean, a dimensionless number which on multiplication by 100 gives the percentage of dispersion with mean. But when we square this ...
3k views

### Can variance be equal to mean?

I understand that variance can be zero if all data points are equal. Can anybody state an example, where sample variance is equal to sample mean and what - if any - is its significance to ...
154 views

### How many samples should be taken to capture the mean and variance of the original set with given error?

I have a set $S$ of $N$ real numbers. I wanna calculate the mean $m$ variance $v$ of $S$. But since $N$ is too large, I do not want to use all of the numbers. Instead, I would like to sample $n$ ...
139 views

### How do I test whether differences in populations are significant?

I'm working on a large database. I want to explore whether certain batch jobs run in more or less time after a change was than they did before the change. There are about 90 distinct batch jobs. They ...
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### Computing descriptives statistics for sites and locations based on literature search with sites having varying numbers of time points

I've collected a data set from the literature. These data are largely binomial: they are clutch sizes of a bird that lays only 1 or 2 eggs in most areas, and in some areas will lay 3. However the only ...