The owners of a company want to summarise the number of annual leave days taken by their employees so far this year. The raw data listed below shows the number of annual leave days that have been taken for a sample of seven staff members.

Leave days taken 7 5 1 18 11 5 3

a) Calculate the variance for this data set.

b) Calculate the value of the interquartile range.

c) Would you describe the variance you calculated in part a) as a statistic or a parameter? Briefly explain your choice.