A Multi-centre, Double-blind, Parallel-group, Randomised Controlled Study to Investigate Efficacy and Safety of Orally Administered BI 425809 During a 12-week Treatment Period Compared to Placebo in Patients With Cognitive Impairment Due to Alzheimer's Disease.

Change From Baseline in Alzheimer's Disease Assessment Scale-Cognitive Subscale 11 Item (ADAS-Cog11) Total Score After 12 Weeks of Treatment

Time Frame: On day 1 (visit 2, baseline) and day 85 (end of trial)

The ADAS-Cog11 is an 11-item cognitive subscale that objectively measures memory, language, orientation and praxis with a total score range of 0 to 70, with lower scores indicating less severe impairment. A negative change indicates an improvement from baseline. Multiple comparison procedures and modelling (MCPmod) in combination with mixed model repeated measures (MMRM) is used for primary analysis of the primary endpoint. MMRM included fixed, categorical covariates of treatment, visit, baseline Mini Mental State Examination MMSE (\>=20, \<20) and treatment-by-visit interaction, as well as the continuous fixed covariates of baseline and baseline-by-visit interaction. Patient was considered as random effect. The unstructured covariance structure was used to model the within patient measurements. The same MMRM model used in the primary analysis is used for the secondary analysis of the primary endpoint.