Critical Reading

The articles in this section come from a series of articles that I wrote for Update magazine in 2005/6 and for Pulse in 2001 as well as a few other articles which are relevant when critically appraising the medical literature.

AKT (Applied Knowledge Test for MRCGP exam)

These are short articles that I have written which may be helpful to anyone revising for the AKT exam. For a more in depth look at Systematic Reviews there is a longer article here.

Visual Rx Example Articles Overview

Clinical Articles Overview

Systematic Reviews Articles Overview

Further Statistics Articles Overview

Evidence & Practice Articles Overview

Vitamin D for people with asthma (Cochrane review 2016)

The Cochrane Airways review on Vitamin D for asthma has been the subject of considerable interest from the press including the BBC Online, Guardian and the NHS ‘Behind the Headlines’.

Vitamin D reduced the risk of emergency department visits or hospitalisation for asthma from 6% to 3% over six to twelve months, and also reduced the risk of less serious asthma attacks from 29% to 18%. These results are illustrated in the Cates plots shown below:

People with an asthma attacks leading to ED visit or hospitalisation


In the control group 6 out of 100 people had a visit to ED or hospitalisation over 8 months, compared to 3 (95% CI 1 to 5) out of 100 on vitamin D (mostly evidence from trials on 658 adults).

People with one or more asthma attacks (as defined in each trial)

In the control group 29 out of 100 people had a study-defined exacerbation over 7 months, compared to 18 (95% CI 10 to 29) out of 100 on Vitamin D (from trials in 658 adults and 341 children).

For full details of the review please follow this link. The evidence from children is still rather limited and we do not know for sure what dose of Vitamin D is needed or what blood level of Vitamin D determines whether people benefit. Vitamin D is not a substitute for normal preventer treatment.

Does treatment make an important difference? (BMJ 2015)

The first question that we can ask when looking at the results of a clinical trial, is whether the results might just be due to the play of chance (with no true difference between the treatment and control). If the likelihood is less than 5% that this could be a chance finding (P<0.05), then the results are regarded as statistically significant. But is the benefit (or harm) from the treatment big enough to be clinically important.

We cannot tell how much difference a treatment makes from the P value! We need to compare the size of the treatment effect with a measure that has been shown to be big enough to make a difference to patients. This is known as the Minimum Important Difference (MID).

It may be tempting to concluded that a treatment that makes an average difference of less than the MID may not be clinically worthwhile. However this is not necessarily so, and if you want to find out more please have a look at the paper by Charlotta Karner and myself published in the BMJ in November 2015.

Cates C, Karner C. Clinical importance cannot be ruled out using mean difference alone. BMJ (Clinical research ed 2015;351(nov20 4):h5496-h96 doi: 10.1136/bmj.h5496