Possible Duplicate:
Finding 99% coverage in Matlab
How can I compute P10, P50 and P90 given an emperical distribution?
Where, P90 means that 90% of the estimates (or outcomes) are expected to be bigger than this estimate. P50 means that 50% of the estimates (or outcomes) are expected to be bigger than this estimate.
If you have the statistics toolbox, prctile does the trick. If your data is X, then prctile(X,[10,50,90]) will return the 10th, 50th and 90th percentile.
If not, just sort the data and take the percentiles using indexing. If X has a small number of entries, be careful with interpolating.