Scores for the two groups were, 2-hour group: 28, 19, 21, 19, 13 Half-hour group: 15, 15, 15, 15, 20 [There are not outliers in either group.] What is the best statistic to summarise the performance of each of the groups? Group of answer choices The mean, as it is the best index of central tendency (when no outliers) The mean, as it is the best index of central tendency in this type of study The mean, as it is the best index of variability The median, as it is the best index of central tendency (when no outliers) The median, as it is the best index of central tendency in this type of study The median, as it is the best index of variability