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How certain are you that this is true? If there is no correlation between any characteristic of interest in a record

Simple. I cannot know what will be inside the file! Because the user may apply the process to any file of their choosing.

So, Just as the polster might discover that the "random selection" they make of the populous, happens to coincidentally consist of the entire membership of some extremist political organisation, they cannot know it will until they take the sample.

Put another way, there may be all manner of correlations, but none of them are known, and so cannot be utilised.

So, at this point, the problem is how to take a statistically valid, random sample of records of any file, without resorting to reading the entire file. I've described the inferences to be drawn elsewhere.


Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.

In reply to Re^6: Random sampling a variable length file. by BrowserUk
in thread Random sampling a variable record-length file. by BrowserUk

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