# Thread: Estimating Mean & Standard deviation from a cumulative frequency curve

1. ## Estimating Mean & Standard deviation from a cumulative frequency curve

How would you go about estimating the mean and the standard deviation from a cumulative frequency curve, if the only data points you know for certain are the 10th, 50th and 90th percentile? I've determined that the distribution is right-skewed, but can't figure out how i would estimate the mean and the sd.

any help will be greatly appreciated!

2. Originally Posted by mathiscruel
How would you go about estimating the mean and the standard deviation from a cumulative frequency curve, if the only data points you know for certain are the 10th, 50th and 90th percentile? I've determined that the distribution is right-skewed, but can't figure out how i would estimate the mean and the sd.

any help will be greatly appreciated!
In what context has this arisen? If it is a home work problem what have you been covering? Do your notes say anything relevant?

I would consider fitting a beta distribution to the given quantiles (though that will still need some side assumptions), but that is not elementary and I will not do it here.

(a triangular distribution is probably easier to handle than the beta - look at the Wikipedia article on the triangular distribution for the cumulatve triangular distribution function.)

CB

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