The standard error of the mean is a value that indicates how close the mean of a data set is to the data set's actual population. It goes along with standard deviation as a statistical measure of how densely located a data set is relative to the mean. A large standard error reflects a data set with a large difference relative to the true mean of a population, while a small standard error indicates that most of the data is clustered around the true mean. Standard error decreases as the number of points in a data set go up, so to minimize the number it is good practice to include as many data points as possible.