Final answer:
To determine scores that mark the middle 68%, one should use one standard deviation from the mean in a normal distribution, since approximately 68% of data falls within this range according to the empirical rule.
Step-by-step explanation:
To determine scores that mark the middle 68%, one should use one standard deviation from the mean in a normal distribution. This is because, in a normal distribution, approximately 68% of the data values fall within one standard deviation of the mean. This is a statistical fact derived from the empirical rule, which is a handy mnemonic related to the normal distribution.
In contrast, the interquartile range (IQR) is used to measure the spread of the middle 50% of a data set, which is not the same as the middle 68%. Therefore, option A (Use the interquartile range) is not the correct way to find the middle 68%. Additionally, option B (Use the range) and option D (Use the median) do not directly help in finding the middle 68% of scores. The range indicates the overall spread between the smallest and largest values in the dataset, and the median only tells us the middle value.
To calculate one standard deviation, you would first find the mean of the data set, and then calculate the average of the squared differences from the mean. The square root of this average gives us the standard deviation.