A while back, we looked at propensity scores as a way of adjusting / controlling for confounders in non-randomised designs. Another approach is the hypothesis-driven estimation of an ‘instrumental variable’: a measurable feature which causes* an outcome to occur through the agency of another. Uh? In the olden days (before smartphones, WiFi and email addresses that […]
Category: stats
StatsMiniBlog: Cronbach’s alpha
When you’re next handing out your questionnaire in clinic, or on the wards, or sit out in the library assessing the results of a recent clinical study, will you be asking about the quality of the questionnaire you’re using or reading about? Of course. I should have realised you will. Though you might just have […]
StatsMiniBlog: Surrogate, proxy or process?
When we look at treatments for children’s ill health, we tend to be stuck in a pleasant dilemma. We normally want to use treatments to stop kids dying, and to make them better quicker – but it’s uncommon for children to die, and they’ll often get better anyway. So we end up using alternative outcome […]
StatsMiniBlog: Will Rogers Phenomenon
The American humorist, Will Rogers, was reported to have said (of the migration of folk from Oklahoma to California): When the Okies left Oklahoma and moved to California, they raised the average intelligence level in both states While this is a deeply unkind comment reinforcing geographical stereotypes, it does a neat job of capturing an […]
Guest Blog: Sampling bias and randomisation
The blog series is expanding! No doubt soley inspired by now running the magnificent @ADC_JC, @davidking83 has taken up the challenge of exploring a critical appraisal nugget/thorn in response to an appraisal session. You too could be part of our team – tweet @ADC_BMJ or find us on Facebook to get in touch – but for now, let’s […]
StatsMiniBlog: Spot on, time and again.
“Spot on!” is a rather anachronistic and very Anglophile phrase, redolent of croquet lawns, tweeds and well designed woven straw hats. It’s no wonder we tend to use – if we are being technical – the word “accurate” instead. But should we be using the word “precise” to make ourselves sound all academic? And what’s […]
StatsMiniBlog: Incidence and Prevalence
There are two relatively simple terms that get splattered about and are sometimes confused and can cause all sorts of difficulties. Incidence – the number of people who develop a condition in a specific period of time. (I think of this a bit like an ‘incident’ – a thing that happened.It probably has the same etymological […]
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 […]
StatsMiniBlog: Z scores.
A recent journal club article, the exact nature of which is irrelevant, triggered a coffee-room discussion on the subject of z scores, which although often understood in relation to Bone Mineral Density reports are otherwise a statistical challenge. In particular the difficulties in interpreting them in a meaningful way were lamented by our team. […]
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 […]