Tagged Questions

The expected value of a random variable; or a location measure for a sample.

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0answers
25 views

Stochastic measuring of Poisson process

Railroad cars' lengths are distributed by $exp(\lambda)$. The train has n cars. We're standing $t$ length units from the beginning of the train, and we are measuring the car's length. What is the ...
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0answers
14 views

When to collapse data on subject level?

I have a question about when to collapse raw data to means per unit (e.g., subjects). In my data I have the following variables: id: subject id ...
5
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3answers
512 views

Can mean plus one standard deviation exceed maximum value?

I have mean 74.10 and standard deviation 33.44 for a sample that has minimum 0 and maximum 94.33. My professor asks me how can mean plus one standard deviation exceed the maximum. I showed her ...
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0answers
7 views

Weighted Standard Deviation [duplicate]

I got a problem calculating a weighted standard deviation for a municipality and its precipitation on various landcover types (LC). I got the mean values of precipitation for several days for each ...
0
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1answer
41 views

Confidence intervals vs P-values for two means

I know in studies where relative risk or odds ratio is calculated, if confidence interval overlaps 1, then the P-value is not significant. Is similar relation true for following situations as well? ...
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0answers
4 views

OOV “frequency”

I'm writing an algorithm to split twitter hashtags into their component words. I'm splitting the tags into all possible substrings, and then looking up each substring's frequency in a dictionary. I ...
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0answers
13 views

Compare two populations by their means… t-test?

I would like to have your opinion on the best way to compare two small sized populations of 13 and 14 individuals (but I have 3 tests for each individual on my dataset, so should I use 13 and 14 or 39 ...
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0answers
22 views

How to find normal quantiles?

A social psychologist interested in eating behavior wanted to divide students into four groups based on their eating proclivities. The four groups were those who were restrained eaters, moderately ...
0
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1answer
34 views

K means clustering of variable with multiple values

I have a sample data below that is from a large data set, where each participant is given multiple condition for scoring. ...
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0answers
35 views

calculate statistical value of the mean of a mean of a mean

EDITED FOR CLARITY Hello, Considering the picture below each values X could be identified by the indeces X_g_s_d_h ...
3
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1answer
27 views

Is the harmonic mean the maximum likelihood estimator for some common continous distribution's parameter?

If $y$ is a vector of continuous data the arithmetic mean is the maximum likelihood estimator for $\mu$ when assuming $y \sim \text{Normal}(\mu,\sigma)$ (not uniquely, of course). The geometric mean ...
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0answers
22 views

What kind of process is this?

For a k-steps stochastic process, assuming that it takes tk mins from the first step to reach the kth step. If we statistic the mean of cost time (tij) from ith step to jth step and the cost time ...
1
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0answers
35 views

What is the mean and variance of this probability distribution?

I don't know if this distribution has a name or not so the best I can do is describe how it is obtained. You start with two arrays of n uniform random variables U(0,1) where n>2. I will provide a ...
0
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1answer
23 views

Can I take the mean of an indirect measurement?

I've been told that one shouldn't take the mean of indirect variables. Specially, I should not give the standard error as the error of the mean. To give an example, if I'm using Ohm's law $V=RI$ and ...
0
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1answer
17 views

If I have estimated set of values, how to get the mean?

I am a beginner in stats and need to get this clear please. I have estimated set of values and need to calculate the mean. Do I still need to divide over N or the sum of all estimated values will be ...
0
votes
1answer
31 views

The difference between the standard error of the sample and the standard error of the mean value

I have an assignment that gives 48 counts of the same phenomena occurring over the same time interval. I am asked to a) Calculate the mean of the counts b) Calculate the standard error of the sample ...
2
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0answers
32 views

Mean and variance of Cox process

Consider the (doubly-stochastic) Poisson point process with rate $ \lambda(t) = \rho e^{-t/\tau} $ where $\rho\sim\Gamma(\alpha,\beta)$ is a Gamma-distributed random variable. I require the mean ...
1
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0answers
38 views

What are the pros and cons of using median imputation to handle missing value?

I have to choose between median or mean imputation to handle missing values. I feel median imputation will work better because it is a number that is already present in the data set and is less ...
2
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0answers
38 views

Sum of Bernoulli random variables

I need some help with a homework assignment. The question I'm given is: "Suppose that $X_1, X_2,..., X_n, W$ are independent random variables such that $X_i\sim Bin(1,0.4)$ and $P(W=i)=1/n$ for $i=1, ...
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0answers
10 views

How do I determine sample size to validate a requirement when I have a lot of margin?

I apologize if a similar question has been asked, but my search has yielded no results. I am having some trouble nailing down the correct methodology to use to design an experiment I am working on. ...
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1answer
41 views

HELP: How to compute a mean for specific cases, NOT the entire dataset! [closed]

I am trying to compute a mean of several variables for just two cases, rather than compute the mean of several variables and include all the cases in the dataset. How does one do this? Thank you for ...
1
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1answer
23 views

Calculating the mean excess loss

Suppose $X$ has the following pdf: $$ f_x(x)=0.01 \qquad for\space 0\le x<100$$ Find the pdf of $X_p$ (the excess-loss variable) and calculate the mean excess loss for $d=10$. \begin{align} ...
2
votes
2answers
59 views

The Mean of the number of times until an event occurs

Lets say we have 6 cards in a hat, that are all red. Now each time, we blindly take a card out of the hat: - If the card is red, we take it out of the hat and insert a blue card. - If the card is ...
0
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0answers
17 views

How to test adjusted mean in R?

I have got eight adjusted means for eight subgroups in a survey study, but I don't know how to test the differences of these eight adjusted means. Any suggestion is appreciated. Thanks!
8
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1answer
222 views

Can we use leave one out mean and standard deviation to reveal the outliers?

Suppose I have normally distributed data. For each element of the data I want to check how many SDs it is away from the mean. There might be an outlier in the data (likely only one, but might be also ...
2
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1answer
125 views

Why does a confidence interval including 0 mean the difference is not significant?

Could someone please explain why zero being inside or outside the confidence interval tells you whether or not the difference is significant?
2
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0answers
20 views

with two EWMA means of different window sizes, can we estimate any other means? slopes? jumps?

EWMA is defined as follows(1, 2, 3, 4, 5): $$ \mu_{N} = \frac {1}{N} \Sigma_{i=1}^{N}x_i $$ $$ =\frac {1}{N} \Sigma_{i=1}^{N-1}x_i + \frac{1}{N}x_{N} $$ $$ =\frac {N-1}{N} \frac{1}{N-1} ...
1
vote
1answer
26 views

Sequence of Random Variables

I am confused about how to approach sequence of random variables that are not identically distributed. For example, consider a sequence $X_1, X_2, \dots, X_n$ with the pdf: $$ f(X_n)= \begin{cases} ...
0
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0answers
50 views

What is the multivariate analog of the median?

There is a univariate mean: sum the points and divide by the count. There is a multivariate mean analog - the centroid, a point in a multidimensional space. (1). For the median one sorts the list ...
4
votes
1answer
167 views

Can the mean lie outside the the interquartile range (Q1 and Q3)? and if so what does it do to the distribution

Can the mean lie outside of the interquartile range? I realize that extreme outliers can affect or pull the mean, but can it pull the mean outside of the interval from the first quartile to the third ...
0
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0answers
20 views

Mean centering variables NOT in a moderation/interaction term [duplicate]

I am trying to assess the impact of multicollinearity in a regression because I have two separately measured variables which have the reversed signs problem (one predictor is +b regression weight, the ...
0
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0answers
19 views

Mean independence and full independence

What is an example of two random variables x and u that are NOT fully independent but such that E(u|x) = 0? Many thanks!
0
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0answers
63 views

Distributions where higher variance in sample estimates leads to smaller loss when estimating mean

Let's say I have an unknown distribution a. I do not know the shape, mean or variance of this distribution but I have access to another distribution ...
2
votes
1answer
30 views

Distribution of Sample Means Compared to Population Mean

Assumptions I have a population (n=5000) and I know everything about it (all point values, mean, standard deviation, etc.) From this, I will sample 1000 items. I can calculate the mean of the sample ...
1
vote
1answer
61 views

how to use arima to do mean model

I am learning arima by this site: http://people.duke.edu/~rnau/411home.htm and I want to get the same result as following notes: ...
1
vote
1answer
28 views

Deriving the formula for the mean of a stratified sample

The formula for the mean of a stratified sample $\bar Y_s$ is: $$\bar Y_s = \frac 1 N \sum_i N_i \bar Y_i$$ where $N$ is the sample size for all strata, and $N_i$ and $Y_i$ are the sample size and ...
0
votes
1answer
54 views

Using Bootstrap to estimate confidence interval of the standard deviation

I am trying to compare two different methods of estimating confidence intervals: a parametric approach that uses the assumption that the sample is t-distributed (i.e. the formulas that are given here: ...
7
votes
3answers
156 views

How can I interpret a plot of trimming percentage vs. trimmed mean?

For part of a homework question, I was asked to calculate the trimmed mean for a dataset by deleting the smallest and largest observation, and to interpret the result. The trimmed mean was lower than ...
1
vote
2answers
79 views

Adding two (or more) means and calculating the new standard deviation

There are a load of discussions online about adding means and recalculating the standard deviation, but on none have I found answer to this question. I have two sub groups with mean $x_1$ and $x_2$, ...
1
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2answers
64 views

Comparing normal with non-normal

I have two sets of data for setup time of a machine, one is setup time when fixture is running alone, another is when another fixture is running alongside. For fixture running alone the data I ...
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0answers
19 views

Mean in Cumulative frequencies distribution

Monthly expense Cumulative Freq. up to 50 7 up to 80 25 up to 120 49 up to 200 58 over 200 60 Calculate ...
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votes
1answer
33 views

Can Coefficient of Variation be used to verify the representativeness of the mean?

I have a sample with approximately 45 million elements, with 4,410 as the mean and 1,657 as the standard deviation. I am not confident whether or not the mean well represents the sample due to the ...
0
votes
1answer
15 views

Correlation on mean values

Please note: the variables named in this example do not correspond with actual variable type values, but are simplified for clarity purposes. I have 13 groups, each containing values X of, say, the ...
1
vote
1answer
77 views

Can I use z-scores in right skewed distributions?

I have a right-skewed distribution that represents that number of "likes" on a certain car category for a number of users. What I am trying to do is a sort of classification based on z-scores. For ...
0
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0answers
17 views

Testing if the mean of one data set is bigger than the mean of the other data set [duplicate]

I have two data sets, i.e., the number of flowers measured in field A and in field B. Each data set has about 40 samples. I want to do a test to check the hypothesis that field A has more flowers than ...
1
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0answers
16 views

Plotting raw data, but running statistics on log-transformed data

My data is non-normal, I want to show my raw data, in a scientific journal, by median +/- mad, to show the true nature of the data. However, if log-transformed, the data is normal. Can I then ...
0
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0answers
12 views

real time object tracking

I have correlation value of object using mean and standard deviation, now i want to normalized that correlation value. how can get normalized correlation in terms of percentage vale?
5
votes
1answer
138 views

$\bar{X}$ versus $\mathbb{E}(\bar{X})$?

I was not able to find this question here, so I am going to ask this: What is the difference between $\mathbb{E}(\bar{X})$ (expected value of $X$ bar) and the actual $\bar{X}$? I am very confused ...
0
votes
1answer
6 views

Best method of estimating the output rate of a group

I have a sample dataset consisting of 2 fields, output volume and input time (in hours) for different persons performing an identical task several times each. What is the best method of estimating ...
0
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0answers
11 views

Histograms With No Final Interval Upper Limit

If you have the following histogram, how do you calculate the mean if you do not know the upper limit of the final interval: ...