Are we active or not?

I'm confused. This is a conclusion that you may well have drawn for yourself, but now it's official. For a little while now I've been gently poking the powers that be, my local authorities and the local Clinical Commissioning Group (the body responsible for primary health care in the area), about the need to challenge modern sedentary lifestyles and get more of us to be physically active. My technique has been to throw official statistics at them, see how they respond and then wonder aloud why they don't. 

In my post - The cost of sitting around in North Yorkshire - I used figures from a project entitled - The Health Impact of Physical Inactivity (HIPI) - which though it originated down in Bristol developed a tool that could be used across the country to estimate the health benefits in four key areas of getting more people to be modestly physically active (150 minutes per week of the sort of activity that raises your heart rate and gets you breathing just a little bit faster). Since this project has now become part of the official body Public Health England I feel free to assume that their work has a seal of official approval. In order to come to their conclusions they needed to have some sort of estimate of how many people currently met this target and to do so relied on survey work carried out by Sport England.

To quote from their report  (Click on the appropriate indicator to give its source)

Adults who are physically active (percentage)

Latest Annual Figure:Estimated number of participants in moderate intensity sport and/ or undertaking some form of physical activity on 20 or more sessions (5 times 30) in the previous 4 weeks, persons 40-79 years, 2010. Calculated using the estimated percentage participation in moderate intensity sport and/ or undertaking some form of physical activity on 20 or more sessions (5 times 30) in the previous 4 weeks, persons aged 16 and over, 2010-2011. 

Comment: Modelled estimates of prevalence, based on survey estimates taken from the Sport England Active People Surveys 4 and / or 5

Source: Health Profiles 2012 

For Scaborough (Click on the relevant bit of the map or select from the drop down menu) the figure they give for those who are sufficiently physically active is a depressing 21%. 

To quote from the Sport England Spreadsheet, used by the HIPI, 

The sports participation indicator measures the number of adults (aged 16 and over) participating in at least 30 minutes of sport at moderate intensity at least once a week.

It does not include recreational walking or infrequent recreational cycling but does include cycling if done at least once a week at moderate intensity and for at least 30 minutes. It also includes more intense/strenuous walking activities such as power walking, hill trekking, cliff walking and gorge walking.

Now a couple of days ago I spoke to the member of the Public Health Team at North Yorkshire County Council who has responsibility for physical activity. He drew my attention to their basic source of public health information across the County - The Public Health Outcomes Framework - and if you open up the page wide enough to see the column for Scarborough you'll notice that the percentage of physically active adults is given as 65.5%. Very different from the 21% given in the HIPI report.

Now the first thing that I remembered about the HIPI data was (see above) that they said it referred to people aged from 40 - 79 and indeed the figure is lower than the overall one given in the Sport England spreadsheet of around 30%. Since this 30% also includes people from 16 - 39 this is what you might expect as people become less active. 

I did try to reconcile the two figures (21% and 65.5%) by getting hold of the population data for Scarborough from the 2012 census, which are available from the Office of National Statistics (go to the third table down), and did some quick sums to find out that the total adult population between 15 and 79 was about 42,000 of whom 14,000 were under 39 and therefore not included in the HIPI data and 28,000 were between 40 and 79. 

If you'll forgive some simple algebra, I attempted to find out what proportion of the under 39's would need to be physically active to make both statements true.

Working in 1000s

42 x 65.5 = 14 x Q + 28 x 21

Therefore 2751 = 14Q + 588

Therefore 14Q = 2751 - 588 = 2163

Therefore Q = 2163/14 = 154.5

So, for the two numbers to be talking about the same thing, 154.5% of the younger age group would have to be physically active. Not so much unlikely as impossible.

Looking at the Public health Outcomes Framework (above), clicking on definitions and selecting the one about physical activity it turns out that whilst their source of information is also Sport England's Active People Survey (see above) their definition of what counts as being physically active is slightly different. I quote:

The number of respondents aged 16 and over, with valid responses to questions on physical activity, doing at least 150 “equivalent” minutes of at least moderate intensity physical activity per week in bouts of 10 minutes or more in the previous 28 days expressed as a percentage of the total number of respondents aged 16 and over.

So, it appears that if you count sessions of between 10 and 30 minutes in your total, as well as those over 30 minutes, then you more than double the number of people considered physically active (from around 30% to over 60%). 

Going further down the Definition page you come across this caveat.

It is not possible to compare results with indicators of physical activity presented in previous publications due to changes in the methods for collecting data on equivalent minutes of physical activity and a wider definition used for what is classed as moderate intensity physical activity.

So, what's happened, to quote from the overview of the spreadsheet that can be found on the Public Health England web site, is that

APS5 collected information on physical activity that was conducted in 30min blocks, while APS6 collected information on physical activity conducted in 10min blocks. This is so that the physical activity measure in APS6 is more in line with the Chief Medical Officer's (CMO) recommendations for physical activity.

So, does this mean that the health impacts highlighted in the original HIPI report were fundamentally overestimated and that the changed definition means we're all a little bit healthier than we thought or does it mean that the target has shifted in order to make it that little bit easier - more realistic - to achieve. I simply don't know.

What I do know though, is that the figure given in the APS6 spreadsheet for the proportion of physically active adults in Scarborough isn't 65.5% but 47.9% and that even if you take it to mean not physically inactive (which the definition given above clearly doesn't) and include those doing between 30min and 150min per week it still only adds up to 64.8%.

So, where did the 65.5% come from.........?

Postscript (13/11/14)

Having chatted to a number of other people with an interest in obesity and physical activity I've done some further checking of sources.

The HIPI report above combined a survey of physical activity levels made by Sport England (under the old definition) with a global study of the increased risk of getting certain diseases if you weren't physically active that had been published in the Lancet. 
(Lee et al Effect of physical inactivity on major non-communicable diseases worldwide: an analysis of burden of disease and life expectancy. Lancet 2012, 380: 219-229)
 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3645500/#R9

Their estimates of increased risk were made by comparing disease rates between active and inactive people, making some corrections for other risk factors, and the figures they used to determine the proportion of the population that was physically inactive came from the World Health Organisation Report. "The Global status report on noncommunicable diseases 2010"
http://www.who.int/nmh/publications/ncd_report_full_en.pdf

On page 96 of this report there's a map showing the global prevalence of physical inactivity on a country by country basis (also give in a table form elsewhere) which it appears that two slightly different criteria  have been used. To quote " Less than 5 times 30 minutes of moderate activity per week, or less than 3 times 20 minutes of vigorous activity per week, or equivalent"

Now since the older CMO's guidance also included the possibility of 75 minutes per week of vigorous physical activity (instead of 5 x 30 min of moderate activity) the figures given for the increased risk of being physically inactive in the HIPI study would appear to apply much more closely to the old definition rather than the new.