Not entirely, big data should be able to extrapolate changes in your activity and make reasnoble assumptions. Big data is 100% rational/logical and has no emotions tied to its decision making, it has idetic memory and will never forget something, and can VERY easily track your standard patterns and identify/track deviations from it.

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Im not saying Bid Data will always know every time for everyone, but just disagreeing with the fact that Big Data will only know after you start searching for pregnancy/child related items.