Total space analysis by Merrifield requires:
Total space analysis by Merrifield;

Requires study casts and cephalograms.
Divides the lower arch into anterior, middle and posterior areas.
The discrepancy for each area is calculated and the resultant value is added to yield the total discrepancy of the arch.

Total space analysis as described by Merrifield is divided into three parts anterior, midarch and posterior.
This is done for simplicity in identifying the area of space deficit or surplus, as well as accuracy in differential diagnosis.
Ref: Graber 6th edition
Study cast and radiograph
Study cast and reference table
Study cast and cephalogram
All of the above