Big Healthcare Data just got bigger. IBM (NYSE: IBM) has spent some $4 billion in the past 12 months to build out its Watson Health division. The latest and largest deal is for Truven Health Analytics, for $2.6 billion. Truven Health provides cloud-based healthcare data, analytics and insights to more than 8,500 clients, including federal and state government agencies, health plans, hospitals, clinicians and life sciences companies. Veritas Capital is making a good $1.35 billion on the sale of Truven, which it acquired in 2012 for $1.25 billion, from Thomson Reuters Corp. (NYSE: TRI).

Truven Health’s extensive data set will be integrated into IBM’s Watson Health Cloud, creating one of the world’s largest collections of health-related data, aggregating approximately 300 million patient lives. Its data informs benefit decisions for one in three Americans.

This is IBM’s fourth acquisition since April 2015, when it acquired Explorys, a portfolio company of Heritage Group, and privately held Phytel. Explorys’ healthcare cloud was one of the world’s largest clinical data sets, representing more than 50 million lives. It was spun off from the Cleveland Clinic in 2009. Phytel developed and sold cloud-based services to healthcare providers and care teams to help them meet changing healthcare quality requirements and reimbursement models. No financial terms were disclosed for those transactions.

Then came the acquisition of Merge Healthcare Inc. (NASDAQ: MRGE) in August 2015, for $1.0 billion. Merge’s technology platforms provides medical image handling and processing, interoperability and clinical systems. Merge shareholders received $7.13 per share in cash, yielding approximately 4.4x revenue and 25.0x EBITDA.

IBM isn’t the only company building huge healthcare data analytics capabilities, but with its Watson super computer, it may be the largest contender in the field. Other companies include Thoma Bravo, LLC, which acquired MedeAnalytics, Inc. in September 2015, and privately held ZirMed, which acquired MethodCare Inc. in September 2014, both for undisclosed prices. MethodCare’s data analytics integrate all patient accounting and clinical systems, with the goal of extracting actionable insights to improve revenue cycle management and, of course, population health management. Earlier that year, 3M Company (NYSE: MMM) bought Treo Solutions, which provides data analytics and business intelligence to healthcare payers and providers.