What is the difference between analogous, parametric, and bottom-up estimating?

Analogous estimating uses actual data from similar past projects as the basis for the current estimate, such as estimating a new building's cost based on a similar one completed last year. It is quick but less accurate. Parametric estimating uses statistical relationships between historical data and project variables, such as cost per square foot or hours per line of code, multiplied by the quantity needed. It is more accurate than analogous when good data exists. Bottom-up estimating estimates each work package individually and rolls them up to a project total.