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Is there any technique to find the median of a large data set using sampling (or maybe randomized algorithms)?

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Of course you can't find the median exactly without examining all the data, but you could use the sample median as an estimator of the population median.

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Thanks Robert. Actually I need to find an estimation of the median (not the actual median). Is there any sample based technique to find such as estimate? –  Hessam Dec 18 '12 at 20:13
    
The question is of course: How good is that estimator? The role of the sample variance for the quality of the sample average as astimator for the population mean is wellknown. What can be said for the error of the sample median as estimator for the population median? –  Hagen von Eitzen Jan 22 '13 at 18:05
    
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