Math Is Fun Forum

benn121

Guest

Calculating the CDF (probability)

Hello,

I have to calculate the cdf F(M) from the data.

Magnitude(m)           Number of events

0 -1                   107
1-2.5                  214
2.5-4.0                108
4.0-5.5                57
5.5-7.0                7
>7.0                   7

[Difficulty]
I basically dont know how to calculate the CDF, do i need to plot a
graph for it or is it some basic formula?

[Thoughts]
So far i have figured out that the word "cumulative" suggests the
role of the CDF function. It sums or accumulates the probabilities
found by means of PDF. The cumulative distribution function F(x) is
defined as follows:

We must sum the PDF over all values of X that occur with nonzero
probability that are less than or equal to x.

fgarb

Member

Registered: 2006-03-03

Posts: 89

Re: Calculating the CDF (probability)

Hi benn,

From looing online, it looks like you're right that the cdf sums the pdf probabilities. Basically, the cdf tells you the fraction of numbers that are less than or equal to some value in your distribution. If you know calculus (if not that's ok too), it represents a definite integral of your pdf from the minimum to your test value.

I'd be very surprised if they expect you to find some function that fits this distribution. Probably if you just make another table where you list the fractions that are less or equal to the values in each bin then that would be good enough.