Diagnosis is a difficult process. A patient who presents to their doctor ill will often undergo a process which involves being asked questions, observed, examined and perhaps even having blood or imaging 'tests'. Each question asked or observation made is either a diagnostic test in its own right or part of one and is a necessary part of arriving at a diagnosis. But some tests are better than others and importantly probably no test is 100% accurate. Sometimes a test result may suggest a patient has normal health when they actually have disease or have disease when they have normal health. This happens to all tests and diagnostic test accuracy research is aimed at evaluating how often this happens, in other words, determining how accurate tests are. Essentially when a clinician decides upon a diagnosis they are consciously or otherwise invoking a probabilistic process where multiple tests are combined and the patient's diagnosis should be the one most probable given the combination of all the test results. However, for this process to be truly beneficial to the patient the clinician needs to know the accuracy of each of these tests and how likely the patient has disease before the diagnostic process has even started. This is where the difficulty lies for those who practise evidence-based medicine. Although the accuracy of many tests has been estimated by research studies, for individual tests the accuracy may vary significantly between studies. This variation may depend on who is applying the test, how it is being applied, which patient it is being applied to and most significantly of all, how the accuracy was measured in the study. When there are several studies there are methods which allow us to combine their results. These methods may also help determine the real reasons why the test's accuracy varies. However, in general, the studies report insufficient data of sufficient quality to enable such analyses to be either possible or comprehensive. Furthermore, from previous work, we have been able to demonstrate that in some cases the test accuracy reported by a study may be virtually impossible in some patient settings. This creates a problem for the doctor. How do they know which estimate of a test's accuracy to use if it varies greatly between studies and risks being nearly impossible for their own practice? We have already begun to develop methods which make it possible to determine whether results from a test study are likely to accurately represent a doctor's practice in general. This would mean that a doctor could confidently apply the research to their own practice without reservation. However, sometimes the research is not reflective of the different clinical settings seen in practice and a more specific solution is required. This may be done by collecting routine data from the doctor's own setting and using it to determine a feasible range of values for the test's accuracy. This method, in its current form, is used to exclude the studies 'least likely' to derive a plausible estimate of a test's accuracy for the doctor in their own practice. At the moment both methods are in development but potentially could be implemented into the real-world and used to improve diagnosis. There are clear patient benefits to improving diagnostic performance including reducing the number of patients treated unnecessarily and increasing the number treated appropriately. One of the aims of this research is to pilot integrating this method into General Practice to help diagnose infection. This could also help reduce the potential for antibiotic resistance by reducing the number of antibiotics prescribed inappropriately. However, before this is done the methods need to be fully investigated to determine their utility and limitations. It may be that other approaches afford greater patient benefit, and an evaluation of these with the methods already described, will be the focus of the proposed research.