A few steps up the career path from data entry, a data processing specialist writes programs to convert data between formats and specifications. Big direct marketing companies use a data processing department to convert their clients' data from whatever format, into something their printers, envelope-stuffing machines, and plastic card embossing machines can use.

The data processing inequality can be used to show that no clever manipulation of the data can improve the inferences that can be made from the data.

Excerpt from Elements of information theory by Cover and Thomas (Wiley).

In short, mutual information can only decrease in a Markov chain, or at best remain unchanged.

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