LAP LAMBERT Academic Publishing Birlie, B: Modeling Time-to-malaria: Comparesion of cox and

In many epidemiological studies time to event data are grouped into strata (or clusters), such as, geographic region, districts, villages and so on. Consequently, cluster specific effects on survival times may cause an extra variation. Under such circumstance, it is substantive importance to draw inference on the nature and magnitude of these effects albeit the primary focus being on survival times. In model based analysis the aforesaid effect (called frailty) are usually accommodated by the use of frailty survival models.