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113
votes
Accepted
Consider the sum of $n$ uniform distributions on $[0,1]$, or $Z_n$. Why does the cusp in the...
From this it is immediate that the cumulative distribution function (CDF) is
$$F_X(x) = \Pr(X \le x) = |(-\infty, x] \cap [0,1]| = |[0,\min(x,1)]| = \begin{array}{ll} \left\{
\begin{array}{ll}
0 & … Because the PDF is the derivative of the CDF, this implies that each time we add an independent uniform variable to $Y$, the resulting PDF is one time more differentiable than before. …
89
votes
Central limit theorem for sample medians
The middle plot is the cumulative distribution function for the same distribution: it uses height to denote probability. It shares its horizontal axis with the first plot. … Let $F$ be the CDF of the original distribution (middle plot) and $G$ the CDF of the Beta distribution. …
81
votes
Accepted
Are CDFs more fundamental than PDFs?
Every probability distribution on (a subset of) $\mathbb R^n$ has a cumulative distribution function, and it uniquely defines the distribution. … The simplest example of a distribution lacking a PDF is any discrete probability distribution, such as the distribution of a random variable that only takes integer values. …
54
votes
Accepted
Why is the sum of two random variables a convolution?
In terms of (cumulative) distribution functions (cdf), it is an operation closely related to the convolution. (See the references.) … The first two of these are special insofar as the box might not have a pmf, pdf, or mgf, but it always has a cdf, cf, and cgf. …
51
votes
3
answers
8k
views
Are CDFs more fundamental than PDFs?
My stat prof basically said, if given one of the following three, you can find the other two:
Cumulative distribution function
Moment Generating Function
Probability Density Function
But my econometrics … How do I know whether a PDF or a MGF can be derived from a CDF? …
45
votes
Accepted
Simulating draws from a Uniform Distribution using draws from a Normal Distribution
Suppose the target distribution has PDF $f$. A value $Y$ is drawn according to another distribution with PDF $g$. … We can accomplish this by fitting the largest possible rectangle (representing a uniform distribution) beneath a Normal PDF. …
29
votes
Weibull distribution parameters $k$ and $c$ for wind speed data
ldots,f_{n}$ and cumulative frequencies $p_{1}=f_{1}, p_{2}=f_{1}+f_{2}, \ldots, p_{n}=p_{n-1}+f_{n}$, then you can fit a linear regression of the form $y=a+bx$ to the values
$$
x_{i} = \ln(V_{i})
$$
$ … Using bootstrap to add pointwise confidence intervals to the PDF or CDF
We can use a the non-parametric bootstrap to construct pointwise confidence intervals around the PDF and CDF of the estimated Weibull …
27
votes
3
answers
112k
views
Finding the PDF given the CDF
How can I find the PDF (probability density function) of a distribution given the CDF (cumulative distribution function)? …
22
votes
1
answer
5k
views
At What Level is a $\chi^2$ test Mathematically Identical to a $z$-test of Proportions?
Equating this to the $pdf$ of the normal (now the $x$ in the $pdf$ will be $\sqrt{y}$ to be plugged into the $e^{-\frac{x^2}{2}}$ part of the normal $pdf$); and remembering to in include $\frac{1}{\sqrt … This formula seems to rely on the binomial distribution. …
21
votes
What does " Y axis" mean in continuous probability distribution?
There are two common ways to represent a probability distribution, the probability density function (PDF) and cumulative distribution function (CDF). I suspect you're wondering most about the former. … For the latter, the distribution is plotted as cumulative from zero to one, so the y-axis is the sum of the distribution up to a given value of x. …
20
votes
Accepted
What's the distribution of $(a-d)^2+4bc$, where $a,b,c,d$ are uniform distributions?
Often it helps to use cumulative distribution functions. … Writing $x=(a-d)^2$ with CDF $F$ and $y=4 b c$ with PDF $g = G^\prime$, we need to compute
$$H(\delta) = \Pr((a-d)^2 + 4 b c \le \delta) = \Pr(x\le \delta-y) = \int_0^4 F(\delta-y)g(y)dy.$$
We can expect …
17
votes
6
answers
5k
views
Probability theory books for self-study
Are there any good books that explain important concepts of probability theory like probability distribution functions and cumulative distribution functions? …
16
votes
Accepted
Distribution of sum of exponentials
Start with the cumulative distribution function (CDF) for $S_2$. … Again, start with the cumulative distribution function (CDF) for $S_2$. …
14
votes
Distribution function terminology (PDF, CDF, PMF, etc.)
Cumulative distribution function (CDF) is sometimes shortened as "distribution function", it's
$$ F(x) = \Pr(X \le x) $$
the definition is the same for both discrete and continuous random variables. … Probability density function (PDF) is a continuous equivalent of discrete probability mass function (PMF). …
14
votes
Accepted
What does Φ mean?
The Phyrexian or Greek letter Φ is being used to describe the CDF (cumulative distribution function) of the standard normal. … The lowercase Greek letter φ is being used to describe the PDF (probability density function) of the standard normal distribution. …