![\"\"](\"https:\/\/blogs.bmj.com\/adc\/files\/2014\/02\/020514_1727_Differentia1.jpg\")
The essential elements of a differential diagnosis study are, like most of critical appraisal, really simple and straightforward.\n<\/p>\nThe essential elements of a differential diagnosis study are, like most of critical appraisal, really simple and straightforward.\n<\/p>\n
You need to start with a bunch of children\/young people who turn up with the symptom, or symptom-complex, you’re interested in. Ideally, you need these folk to not already be known to have something, to attend a similar type of facility (e.g. office for general practitioners, or ED for ED types), and to be a consecutive group or random sample.
\n\n<\/p>\n
(If they are already known to have something, there can be a sort of “detection” bias \u2013 where if you know someone had Gilbert’s syndrome you may be more able to detect the jaundice than if you didn’t. If they are at a different level of referral, you may well see s different spectrum of illnesses, either aetiologic or of severity \u2013 for example lethargy and weight loss seen at a GP surgery and in an oncology outpatient clinic. The sampling aspect is about how the group may reflect the general population; non-random, non-consecutive samples can be ‘selected’ \u2013 so if you’re looking at joint tenderness, and there are no nighttime or weekend attendees, the diseases diagnosed may have a lower proportion of acute traumatic or infectious causes than if you’d sampled differently.)\n<\/p>\n
You need to be able to have a convincing way of making a ‘final diagnosis’ for each patient in this group. Without this, you end up with a list of possible and maybe and no amount of fancy stats will get you out of this.\n<\/p>\n