Such observations are said to be quantitative.
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This depends on what you are observing, but since number and amount are both measurements of quantity, they are somewhat interchangeable. Observations usually deal with both, because an observation is the action of observing something to collect information, and most information has to be quantified in order to be useful. And when quantifying something, a number or an amount has to be used.
Qualitative (quantitative are observations that can be expressed numerically)
qualitive
Manipulative observations
qualitative observation