Final answer:
The mode can sometimes be determined by simple observation of the most frequently occurring value, while the mean, median, and standard deviation require explicit calculation post data evaluation.
Step-by-step explanation:
The question you asked pertains to the concepts of mean, median, mode, and standard deviation, which are statistical measures used to describe a data set.
Specifically, the question seeks to identify which of these measures is not determined until after a sample is tested and evaluated.
All of these measures, with the exception of the mode, require calculation after data collection.
However, the mode can sometimes be seen from a simple inspection of the data if there is a value that clearly appears more frequently than others.
Among the options given, mean, median, and standard deviation indeed require explicit calculation post data evaluation.
Therefore, while all four measures necessitate having a sample, mode is the one that might be observable without thorough statistical computation.