The time horizon of a study refers to the study duration or length of follow-up for data collection. The time horizon for a comparative evaluation should be long enough to capture the stream of relevant health and economic effects that are sufficient to detect any differences in these between the intervention and control groups. To not do so may yield misleading findings.
One of the challenges of telemedicine evaluations derives from the novelty of telemedicine applications. It is inevitable that provider institutions, physicians, patients, and other participants will require some time and practical experience to gain familiarity and skill with these applications. As such, some time will be required to "get up the learning curve" for these applications, with corresponding changes in efficiency and satisfaction. Study durations that begin during this ramping-up period may yield misleading results. Similarly, given the inefficiencies of resource use that arise when installing any new technology or program, the costs of operating a start-up telemedicine operation will not reflect the true, longer-term running costs of the program. In the case of rapidly evolving technologies, such as those used in telemedicine, the costs can change during the course of a study. The results of evaluations of cost or cost effectiveness of telemedicine operations can be very sensitive to the time spans for depreciation of capital costs and other accounting techniques for spreading costs over time.
The time horizon of a comparative evaluation of telemedicine should depend upon the endpoints or outcome measures of interest. Determining how teleconsultations change access to services may not require long follow-up periods, particularly if they are made available to large populations. However, it may take enough time to secure multiple visits for individual patients to gauge their satisfaction, and sufficient time for clinicians to become familiar with teleconsultations with a variety of types of patient indications to get a reliable measure of their respective levels of satisfaction.
Any evaluation of telemedicine that is intended to determine its effect on health outcomes must be long enough to capture the disease episode (for acute conditions) or normal course and fluctuations of disease (to capture changes in chronic conditions). Even longer follow-ups may be required to capture data on how the use of telemedicine can avert downstream progression of disease and adverse health events and their associated health care costs. Following up on longer-term health outcomes may require a more concerted tracking effort, including capturing patient data at multiple sites of service. Of course, increasing the time horizon of an evaluation generally increases its costs, and such evaluations are subject to cost constraints. Further, managers and policy makers usually seek study findings sooner rather than later, so there often is pressure to complete evaluations in as short a time as possible. Therefore, telemedicine evaluations should provide a rationale for how the time horizons correspond to the endpoints or outcomes of interest and any relevant constraints.