Tagged Questions

2
votes
1answer
222 views

method of moments with variance=$\sigma^2$

I am trying to estimate the value of a parameter by equating variance from a distribution to the sample variance... i.e. using method of moments estimation. Would it better to use the variance formula ...
2
votes
1answer
186 views

Where did this risk exposure 'estimation-formula' come from?

I was reading a book and the authors metioned that risk exposure can be estimated scientifically using this forumula: $risk(\$) = \frac{(a + 4m + b)}{6}$ and standard deviation $\sigma = ...
0
votes
1answer
267 views

Mean and standard deviation of Gaussian Distribution

I have some random numbers which are generated from Gaussian Distribution. But I don't know the mean, standard deviation of that distribution. How can I find them using random numbers?
2
votes
0answers
78 views

If I take n-standard deviations of my data what would be my confidence level with the estimate?

I have some measurement data of estimates vs actuals (of some metric $m$). For every such data I also have the ratio of $\frac{actuals}{estimates} = r \space (say)$ - if this ratio is greater than 1 ...
6
votes
1answer
121 views

Estimating the functional form of the slowly time-varying variance of a Gaussian process

Consider the following simple set-up. In the interval $[0, 1]$ we are observing the realizations of independent normally distributed random variables at times $t_1,\ldots, t_N$. The r.v. $X(t)$ has ...
9
votes
2answers
3k views

Why is sample standard deviation a biased estimator of $\sigma$?

According to the Wikipedia article on unbiased estimation of standard deviation the sample SD $$s = \sqrt{\frac{1}{n-1} \sum_{i=1}^n (x_i - \overline{x})^2}$$ is a biased estimator of the SD of the ...
2
votes
0answers
93 views

Calculate error for monthly exchange rates

I'm working on a project that will convert $USD to other currencies. The system will use average monthly exchange rates instead of daily because of pre-existing limitations. I need to calculate an ...
1
vote
1answer
158 views

Expected number of shipments and its standard deviation

Recent history suggests that one supplier fails to meet this new specification 20% of the time. Assume that the next 15 batches of this alloy are a random sample. How can I find the expected number ...