Statistics are single values that summarize the information from a set of data. Summary statistics (like the mean and range) are especially useful for getting an initial sense of how samples from two groups (levels of a categorical variable) compare. This can also be helpful for identifying erroneous values in your dataset. The mean is the sum of all individual measurements divided by the total number of observations. The median is a typical observation taken from the middle of the range of observations. Sometimes, if there is a large amount of variability between your observations, you might use the coefficient of variation, which is the standard deviation divided by the mean. This will give you a better expression of the extent of the variability if you are comparing two sets and the means are similar.

CV= (standard deviation/mean)

The standard deviation is the square root of the variance. It is the most commonly used measure of spread. An important attribute of the standard deviation is as a measure of spread. In a normal distribution, about 68% of the scores are within one standard deviation of the mean and about 95% of the scores are within two standard deviations of the mean.

The standard error of a method of measurement is the standard deviation of the sampling distribution associated with the method.