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  2. Why is the sum of two random variables a convolution?

    stats.stackexchange.com/questions/331973

    In terms of probability mass functions (pmf) or probability density functions (pdf), it is the operation of convolution. In terms of moment generating functions (mgf), it is the (elementwise) product. In terms of (cumulative) distribution functions (cdf), it is an operation closely related to the convolution. (See the references.)

  3. This is because a probability density assumes a continuous variable, where the probability over any single point is 0, but over an interval, we can calculate probabilities via integration. Discrete random variables have probability mass functions (PMF) , which assign probabilities directly to specific values.

  4. Here, c1=-1.2848 and c2=6.7046. @wolfies ignored c1 (it likely will be too far in the tails of the probability density functions to matter (especially if we round to just a few decimal points)). The more correct way is to find both c1 and c2, and to find the area of overlap of both functions:

  5. For the latter, the distribution is plotted as cumulative from zero to one, so the y-axis is the sum of the distribution up to a given value of x. For a probability density function, there's a big hint in the name: it's a density. You're right, though, that we don't often think of this Y-axis as all that important.

  6. What is the reason that a likelihood function is not a pdf?

    stats.stackexchange.com/questions/31238

    A probability density function (pdf) is a non-negative function that integrates to 1 1. The likelihood is defined as the joint density of the observed data as a function of the parameter. But, as pointed out by the reference to Lehmann made by @whuber in a comment below, the likelihood function is a function of the parameter only, with the data ...

  7. How to find the mode of a probability density function?

    stats.stackexchange.com/questions/176112

    A mode of a continuous probability distribution is a value at which the probability density function (pdf) attains its maximum value So given a specific definition of the mode you find it as you would find that particular definition of "highest value" when dealing with functions more generally, (assuming that the distribution is unimodal under ...

  8. It might help you to realise that the vertical axis is measured as a probability density. So if the horizontal axis is measured in km, then the vertical axis is measured as a probability density "per km". Suppose we draw a rectangular element on such a grid, which is 5 "km" wide and 0.1 "per km" high (which you might prefer to write as "km$^{-1

  9. 3. I have read a lot about density functions, but what I am missing is how to create a density function if you have continuous values in data. For example, I have data with negative and positive values: Data = (−20, 30, 21.4, 2.3, −4.5). Data = (− 20, 30, 21.4, 2.3, − 4.5). My goal is to create a function, from which I could do a ...

  10. A good example is the Bernoulli(p) distribution: its distribution function at x equals 1 − p when 0 ≤ x <1 and otherwise is 0 when X <0 or 1 when X ≥ 1. It has no density. The paper is concerned about situations like a bivariate random variable (X, Y) where X has a standard Normal distribution and Y = X. This is perfectly well defined; it ...

  11. 4,046 4 27 58. 1. The sampling distribution of a mean often has no probability density at all. For instance, the mean of a sample drawn from a discrete distribution will itself have a discrete distribution. – whuber ♦. Sep 9, 2018 at 22:38. @whuber, Dear whuber, thanks.