Scientific speculation occurs when premature conclusions are formed without fully interpreting and checking observations and experimental procedure for possible sources of error.
Speculation in scientific fields is avoided by most professionals when there is insufficient evidence to make conclusions about observed evidence. "Clever Hans" is a prime example of the importance of scientific skepticism and the importance of careful review and exhaustive testing. While many believed the horse could preform mathematics, Oskar Pfungst proved that the horse was simply reading the subtle body language of the person asking the question. Premature conclusions are often inaccurate, and can lead to further inadequacies in future tests.
"... our experience with real scientists and engineers indicates that when they're on-the-record, top-notch scientists and engineers won't even speculate about the color of their socks without looking at their ankles1. They have top-notch reputations because they're almost always right. They're almost always right because they keep their mouths shut until they've fully analyzed the data."