Final answer:
The Coefficient of variation is the measure that best represents the risk to reward ratio for an investment over a specific time period.
Step-by-step explanation:
Among the options provided, the measure risk to reward earned by an investment over a specific period of time is best represented by the Coefficient of variation (Option A). The coefficient of variation is calculated by dividing the standard deviation of the investment's returns by the mean (expected value) of those returns.
This statistic provides information on the degree of variability in relation to the average return, thus reflecting risk in comparison to the potential reward. Option B, Market deviation, is not a commonly used term in this context. Option C, Standard deviation, measures the variability of returns, but does not directly relate it to the reward. Lastly, Option D, Total variation, is a broad term, and not one that specifically measures risk to reward ratio.