$3$ points do we calculate indirect cost rates over longer periods $,$ such as a year $?$ longer the period $,$ the smaller is the influence of seasonal patterns on the amount of opportunity costs longer the period $,$ the greater is the influence of seasonal patterns on the amount of costs shorter the period $,$ the smaller is the influence of seasonal patterns on the amount of opportunity shorter the period $,$ the greater is the influence of seasonal patterns on the amount of costs