Who do you believe?

Further to Monday's post about the childhood asthma rate in Scotland, it is worth comparing the data presented by Jill Pell in her NEJM paper—which claimed there were 18% fewer hospital admissions after the smoking ban—with the actual hospital admissions data recorded by the Scottish NHS.

This is the "smoothed" graph presented by Pell in her study, which as noted in a previous post, does not even fit her own data. (The last 'year' shown is also not a full year.)

Pell's study produced the intended flood of media coverage, of which this Reuters report was typical.

Scottish smoking ban cuts childhood asthma attacks

A 2006 public smoking ban in Scotland reduced the number of serious childhood asthma attacks by 18 percent per year, researchers reported on Wednesday.

Before the ban imposed in March 2006, the number of hospital admissions for asthma was rising by 5 percent a year among children under 15. The after-ban benefits were seen in both pre-school and school-age children.

Critics had said the ban could force smokers who could not light up in the workplace or in enclosed public spaces to smoke more at home, increasing the risk to children.

Dr. Jill Pell of the University of Glasgow, who worked on the new study, said the findings in the New England Journal of Medicine show that did not happen.

"The evidence we have from Scotland is that it had the opposite effect. People are generally more accepting of the need to protect nonsmokers and vulnerable groups such as children," Pell said in a telephone interview.

"Children were being exposed to less secondhand smoke. We went into the study hoping we would see some health benefit coming out of that."

However...

NHS Scotland has since published the statistics showing how many children were admitted to hospital with asthma between 2005 and 2009. These figures can be viewed here. They do not support Pell's hypothesis in any way, shape or form.

The graph below shows the rate of hospital admissions for asthma for children aged 0-14 years in all Scottish hospitals (per 100,000). The years shown are financial years (April to March - the first year shown is 2005/06), which is useful since the smoking ban was introduced in Scotland at the end of March 2006. Each of the last four bars therefore represent a full post-ban year.

The next graph shows the total number of episodes of the same (ie. the absolute number of admissions). It naturally shows a very similar picture.

Although not discussed by Pell, it is interesting to note that the rate of asthma admissions amongst people of all ages has been higher in every year since the smoking ban was introduced.

And, for good measure, let's have a look at hospital admissions for all diseases of the respiratory system combined.

The data available online do not go back further than 2005/06 so we cannot see the long-term trend earlier in the decade. However, it is sufficient to see that there was no decline in hospital admissions for any of these diseases amongst any age group. If anything, there was an increase.

So, once again, you have a choice. You can choose to believe Jill Pell, a researcher who has, shall we say, "form" when it comes to producing studies like this.

Or you can believe the statistics produced by NHS Scotland which are based on the number of people who actually got admitted to hospital. These statistics, incidentally, support the claim made by Asthma UK that the rate of childhood asthma has remained essentially static for a decade.

It's your call.