## Basics: AVID

The shortcut world of acronyms for critical appraisal was lacking one for diagnostic test accuracy – we have RAMbo for RCTs, FAST for systematic reviews, but what of the poor reader of studies evaluating a new test? We know the basic idea – patients who are considered to potentially have the diagnosis in question have […]

## When a test isn’t a test

There are many reasons why we request tests, in medicine. One imaginary patient’s journey picks up a number of them. Take a patient who presents with a painless lump on their arm, who’s tired and a bit pale & washed out. You might send a series of blood tests, including a full blood count to […]

## StatsMiniBlog: ROC plots

A (while ago) we published an explanatory page about ROC plots in the Education and Practice journal. There are a few great reasons why we should replicate it here: 1. So people can read it more easily 2. Because it fits into the stuttering series on diagnostics 3. It saves me having to write the […]

## Springing into action

If you could get a multiplex PCR result back to you within 2 hours that told you your hot, grumpy, 2 month old patient did not have bacteraemia, would you discontinue antibiotics? How sure would you need to be of that result – 95% certain? 98% certain? 99.5% certain? What – in diagnostic analysis speak […]

## Gambling, alcohol and division.

No, not an average afternoon at the Houses of Parliament, but another in our diagnostics series. Moving yourself from looking at the predictive values of the tests as evaluated, to taking this information but using it in the situation you face, is a case of Bayesian mathematics. Which sounds hard. But its absolutely what you […]

In a previous post I muttered about how unhelpful sensitivity and specificity are to practicing clinicians, and how what we really want to know are the predictive values of a test. Remembering the Table       Really diseased Really not diseased Test +ve A B 1.. A/(A+B) Test -ve C D 2.. C/(C+D) 5.. […]

## Sensitivity and specificity

Sensitivity and specificity are those sorts of things that can really get knickers twisted up something rotten. They sound like something you should be able to understand, they get used as if you understand them, and then you realise … it’s not quite as you thought …   Really diseased  Really not diseased    Test […]

## Diagnostic test accuracy

The main things we look for when examining a new diagnostic test are “Is it as good as, or better than our usual one”, “Is it quicker?”, “Is it cheaper?” and “It is easier for patients/less dangerous?” While the latter three questions can be assessed by asking the folk who do the test, asking the […]

## Differential Diagnosis

The essential elements of a differential diagnosis study are, like most of critical appraisal, really simple and straightforward. 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 […]

## Testing. Diagnostic tests – why?

“But what’s wrong with him, doctor?” The constant refrain from many a consulting room is not “How can you make her better?” but “Can you name the problem so I can own and understand it?”. When addressing this need we will each develop our  own approaches; some of us will explore differentials, others state the […]