HTA (Health Technology Assessment) is the procedure that weighs whether a new treatment (drug or other 'intervention' (e.g. device, surgery, etc...)) is beneficial compared to current therapy. The QALY (Quality adjusted Life Years) is an 'objective' measure to quantify the improvement of the new therapy, and is a calculation that takes into account the additional life-span (in years) and the 'quality of the life' (QoL) of the patient (1 being optimal, 0 being 'no quality' (= death)).

Example: if a new treatment increases the average lifespan with 5 years, and the QoL is improved from 0.5 to 0.8, then the QALY of this treatment is 5*0.3=1.5

The ICER (incremental cost effectiveness ratio) is a value that calculates the cost for each QALY obtained. Mathematically:

ICER = differences in costs / difference in QALY

With 'differences in costs', the differences between the old therapy (or no therapy at all if no therapy existed) and new therapy is meant.