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

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21 views

Finding two independent means in a collection of data

I have a process that supposedly can run in two different modes with executions times of T1 and T2 respectively. Also the process runs in one mode more often than the other. The process is a computer ...
0
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0answers
18 views

How to compute the average of the relative weightings?

I have the following problem. I have a sample of daily snapshots of a portfolio grouped by four asset classes: Forex, Futures, Options and Equities. For each day in my sample I compute the weight of ...
1
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1answer
36 views

Understanding “the kernel has zero mean”

I am trying to understand kernel density estimation and found the graphic below illustrating different kernel functions on Wikipedia. I have no trouble reconciling it with the two statements "the ...
0
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0answers
53 views

Confidence interval of the mean for a beta distribution when alpha and beta are estimated [duplicate]

I have elementary knowledge in statistics. I'm trying to estimate the confidence interval for mean of a beta distribution as specified in this article using log likelihood estimation given alpha, beta ...
0
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0answers
40 views

threshold based on mean and standard deviation

I have a time series of 70000 data points. I want to separate samples of this time series which have very large values as compared to the time series. How can i threshold sample to separate. What i ...
0
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1answer
19 views

Comparing mean differences between groups when standard deviation in one of them is 0

I was wondering if it is possible and -if yes- what are the implications when one is trying to compare mean group differences of a continuous variable that varies in one group but is a constant number ...
1
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1answer
32 views

AUC per time is nothing else than the mean?

Using AUC is in vogue and has found his place also in clinical research (example). What I don't understand is AUC per time. For example, if a clinical or psychological parameter is measured over time. ...
0
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1answer
20 views

Statistic test when bias is not random

Is there a statistical test that I can use to say that there is bias in the result of my analysis but the bias only occurs at certain region. The scatter plot below probably will make more sense: ...
5
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2answers
51 views

Independence of Sample mean and Sample range of Normal Distribution

Let $X_1,\dots,X_n$ be i.i.d. random variables with $X_1 \sim N(\mu,\sigma^2)$. Let $\bar X =\sum_{i=1}^n X_i/n$ and $R = X_{(n)}-X_{(1)}$, where $X_{(i)}$ is the $i$ the order statistic. Show that ...
1
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0answers
42 views

How do I solve this problem? Novice here

Here's the problem. I work for a transportation company and we're trying to prove the following hypothesis: Drivers are allowing passengers on the vessel without taking taking their paper boarding ...
0
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0answers
29 views

How to plot mean plus/minus standard deviation for histograms?

I have a set of grayscale images, where the pixels may have values in the range $[0, 255]$. From each image, I calculate a histogram, which shows how many pixels have the value $0$, $1$, $2$, and so ...
8
votes
1answer
381 views

Is the median a “metric” or a “topological” property?

I apologize for the slight abuse of terminology; I hope it will become clear what I mean below. Consider a random variable $X$. Both the mean and the median can be characterized by an optimality ...
1
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0answers
52 views

How to calculate mean and standard deviation of a range variable (grades) when the raw data is based on frequency categories?

Results of an exam indicate that: 13% of the class earned an A 20% earned a B 48% earned a C 10% earned a D 9% earned F's The grade C ranges from 70-79%. Assuming that the data is normally ...
-1
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0answers
43 views

How to find Bayesian average

I am trying to understand Bayesian concept. Apparently, the final value is dependent on prior estimate of value. So, for the simplest situation of finding average of following series of numbers, how ...
1
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3answers
43 views

How many samples needed to approximate true mean?

If I have some arbitrary random variable with true mean $\mu$ how many samples from its distribution do I need to take such that the empirical mean $x$ approximates $\mu$ within an error of less than ...
6
votes
1answer
96 views

Efficient way to compute distances between centroids from distance matrix

Let us have square symmetric matrix of squared euclidean distances $\bf D$ between $n$ points and vector lengthed $n$ indicating cluster or group membership ($k$ clusters) of the points; a cluster may ...
0
votes
1answer
45 views

Making the most of Standard Deviation and P value — graphing?

I have a question or two in regard to getting the most out of the statistics of my data. By way of background, my qualitative observations of two distinct populations that are uniformly regarded to be ...
0
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1answer
44 views

In SPSS, should I calculate the mean score or the total sum score?

Are there any differences between mean scores and total sum scores? I know how to calculate both, I just don't know if there is one of them that is preferable? Also, the scores will be used for ...
1
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1answer
33 views

How do you run correlations on mean values?

I have five random variables measured on units in four sites, and I'm interested in comparing between sites to determine if there are significant differences. I'm extremely interested in the ...
3
votes
1answer
41 views

Is it correct to use plus or minus symbol before standard deviation?

I have represented standard deviation as "±SD" before in publications. But I like to have opinions on this. Is it appropriate to use the notation '±' with SD ? Or is it only for Standard error ?
0
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1answer
15 views

Hypothesis significance better than Mean Average Precision?

Consider I have two search engines, one (B) with Mean Average Precision higher than the other (B). Now, can this metric be enough to say that the first search engine A is better than the second one B? ...
0
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0answers
18 views

how to estimate scale variance only using item sd's and scale reliability

The problem I encounter is that I need to estimate the scale variance of a psychometric scale without having the original data. The only information I have is the means of the (binary) items, their ...
0
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1answer
24 views

How to test if one mean is greater than the other in R?

What would an appropriate test be for testing whether group 3 has a larger vital capacity than group 1 from the vitcap dataset in the ISwR package. This is what I was thinking so far, but I'm really ...
1
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1answer
32 views

Is this the correct way to calculate the mean and variance of $(X-n)/(2n)$ where $X$ follows a Chi-squared distribution with $n$ degrees of freedom?

Let $X_n$ follow a Chi-squared distribution with $n$ degrees of freedom. I would like to study the variance and mean of $$\lim\limits_{n \rightarrow \infty} Y_n := \frac{(X_n-n)}{(2n)}$$ I would also ...
1
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1answer
95 views

how to calculate expected sample scale mean and sd based on the means and sd's of its dichotomous items?

I am developing a new psychometric scale consisting of a several dichotomous items taken from a larger item bank. The p values (item means) are known. Now I need to calculate the expected mean and ...
5
votes
3answers
337 views

Expected number of dice Rolls require to make a sum greater than or equal to K?

A 6 sided dice is rolled iteratively. What is the expected number of rolls required to make a sum greater than or equal to K? Before Edit ...
0
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1answer
22 views

Deriving the mean from a raw and standardized score

My son has received 52 marks in a test. This has been standardized, using a mean of 100 and a standard deviation of 15, as 102.27 What is the mean mark, and how many marks would he have needed to get ...
0
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0answers
23 views

Descriptive and Inferential Statistics

I am doing a time series analysis (stock market returns) and I am currently looking at the summary stats. I know the definitions of the individual stats but the one I am stuck on is the relationship ...
0
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0answers
18 views

mean of clients during a specified time interval

I would like to calculate the mean number of guests in a restaurant for example, during one week. I have two cases: 1- we take measures of number of guests each 5 minutes, 2- we take measures each ...
0
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0answers
25 views

What would be null and alternate hypothesis

A photoconductor film is manufactured at a nominal thickness of 25 mils. The product engineer wishes to increase the mean speed of the film and believes that this can be achieved by reducing the ...
1
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1answer
30 views

Calculating Mean and Standard Deviation From Frequency Chart

I have only a frequency table like that below. How can I get the mean and standard deviation? ...
0
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0answers
8 views

Calculating daily mean for whole year through temporally varying samples

I have really basic statistical question about calculating the mean of two temporally different datasets. Let's say that we have two spatially and temporally varying datasets from the same measurment ...
2
votes
0answers
18 views

Distribution with fixed mean and closest to a given distribution

I was wondering if this problem has been tackled in some way in the probability/functional analysis literature: Given a pdf $f$ such that the expectation is zero and $\mu\in\mathbb R$, find the ...
0
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0answers
25 views

What sample size is needed to estimate the population mean, with unknown variance?

I want to know what's the sample size needed to estimate the population mean, with unknown variance? I'm filling up a database that stores the values of wifi-accespoints' strength level at certain ...
0
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0answers
9 views

Permutation test for 3 variates

I have 3 covariates, which are merely count data. They have 3 different means. How can I get a unique p-value or how can I compare them? The aim of my study is to know if those populations are ...
2
votes
1answer
20 views

How do I calculate PERT stddev if I use custom weight factors?

According to (for example) http://tynerblain.com/blog/2006/04/13/foundation-series-basic-pert-estimate-tutorial/, the PERT mean estimate is $$\text{meanA}=(\text{optimistic}\ +\ 4 \times ...
0
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0answers
53 views

Meta-Analysis Data Extraction Process - Reporting of Outcome Measures

I am conducting a Meta-Analysis of a clinical intervention in randomised trials. I am using the RevMan Software of the Cochrane Foundation. The problem regards the extraction process of relevant ...
1
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1answer
47 views

How to compare means, variances and standard deviations of durations for statistical significance

I am trying to compare multiple mean values, variance and standard deviation values for statistical significance. For example I have the following data: Data 1 Mean: 0.01304 Sample ...
0
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1answer
27 views

Confidence Interval For Mean By Bootstrapping

The standard deviation in my original sample is very large, about 100 or so. I took many bootstrap samples, found the mean of each bootstrap sample and then took the mean of these means. I found the ...
1
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0answers
33 views

How to calculate E(1/Y) when Y is Inverse Gaussian distributed?

The Inverse Gaussian Distribution density is : $$\frac{\phi^{\frac{1}{2}}}{\sqrt{2\pi y^3}} exp[\frac{-\phi(y - \mu)^2}{2\mu^2y}]$$ Got to this integral: $$\int_0^\infty \frac{1}{y} ...
2
votes
2answers
51 views

Is recoding a categorical variable into a continuous variable possible?

I'm trying to see if it's possible to recode a categorical variable into a continuous variable. The data would probably not permit it but what if I really needed to find the mean and SD? Is there ...
1
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1answer
23 views

How to identify a binary model with varying mean and variance

I have the following model, Yi = 1.( Xiβ + εi > 0) where εi~ Ɲ(Ziδ,1). or Yi = 1.( Xiβ + εi > 0) where εi~ Ɲ(0, (µ + Ziδ)2) with a binary model, can i identify β and δ in such a model? How? and ...
1
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1answer
34 views

Is it possible to compute the mean/median of an variable by a contingency table?

A contingency table contains the frequencies of two discretized variables. To be more specific, the discretization is done by splitting the spectrum of a signal into equal width intervals. Is it then ...
0
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0answers
30 views

Can anyone help interpreting this equation?

The following is a portion of text from the Heckman, Ichimura and Todd (1997) paper about propensity score matching in ReStud The matching methods discussed in this paper focus on estimating an ...
0
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1answer
13 views

Estimating population mean when using biased sampling?

Say you had a sample of 50 items that was constructed by taking selecting values that were in the top 75% (not in the first quartile), and you had to take 61 items to find those 50 (11 were in the ...
0
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1answer
24 views

Using the average as a cut off to group data and compare groups?

I measured cell size of human muscle and I wanted to examine the effect of age on the parameter. I graphed my data as a scatter plot and calculated Pearson's correlation coefficient but then also ...
0
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0answers
18 views

Time-partitions of sample size

I am struggling with explain something I read in a Whitepaper. The essence is as follows. Let's begin with a random variable $X$ defined as number of events in an hours. Further, we assume that $X ...
2
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2answers
105 views

Which is better, replacement by mean and replacement by median?

I'm doing a project that involves replacing missing values in a set of data (first time doing this). This is involves using to methods "replacement by mean" and "replacement by median" to fill in the ...
0
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1answer
49 views

Mean vs. Standard deviation for data ranging between 0 and 1

If e.g. 100 people can rate a subject between 0 and 1 than the dispersion (e.g. standard deviation) among the 100 raters is potentially largest for a mean of 0.5 (50 people rate 0, 50 people rate 1) ...
9
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2answers
216 views

Does a prediction interval have to contain the mean?

I am having a huge problem with a conceptual problem that I came up with. Say a company has a distribution that is highly skewed. Something similar to an exponential or lognormal only more extreme. ...