Architecture types remain various. However, in 2017, Roehrs et al. performed a systematic literature review of PHRs and were able to divide architecture types into two groups: model-based and coverage-based. Model architectures represent more traditional takes on PHRs, including health data that is still stored on paper. Coverage architectures represent more hybrid takes on the PHR, "with the PHR distributed inside and outside the health care organizations" based on the data's physical location. The associated architectural types have different costs and benefits. Likewise, stand-alone, provider-tethered, and payer-tethered PHRs have different advantages and disadvantages for patients related to their individual circumstances. Such differences are among the priority areas in PHR research. As PHRs may play a key role in advancing health information exchange, interoperability with other health IT systems is an important consideration for PHR architecture. Additionally, PHR systems requires users to put forth an "'ongoing' effort to keep their account up to date" (maintain an active role in managing their own health), which in turn requires further examination of PHR architecture and adoption models by developers. Delivery platforms One of the principal distinguishing features of a PHR is the platform by which it is delivered. The types of platforms include: paper, electronic device, and web. Paper Personal health information is recorded and stored in paper format. Printed laboratory reports, copies of clinic notes, and health histories created by the individual may be parts of a paper-based PHR. This method is low cost, reliable, and accessible without the need for a computer or any other hardware. Probably the most successful paper PHR is the hand-held pregnancy record, developed in Milton Keynes in the mid-1980s and now in use throughout the United Kingdom. These include the Scottish Woman-Held Maternity Record, All Wales Maternity Record, and Perinatal Institute notes. Paper-based PHRs may be difficult to locate, update, and share with others. Paper-based PHRs are subject to physical loss and damage, such as can occur during a natural disaster. Paper records can also be printed from most electronic PHRs. However, Fawdry et al. have shown that paper records are extremely flexible and do have distinct advantages over rigid electronic systems. Electronic devices Personal health information is recorded and stored in personal computer-based software that may have the capability to print, backup, encrypt, and import data from other sources such as a hospital laboratory. The most basic form of a PC-based PHR would be a