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Glimmer of hope XXII

Weight gain and lockdown: empiricism vs. physical modelling



Life in lockdown has disrupted our daily lives, creating the perfect setup for putting on pounds. In a poll of 1,000 people, nearly half of the women and almost one-quarter of the men reported that they had gained weight “due to COVID-19 restrictions”. I presume all 1,000 have good, quantitative observational time-series of their weight change.

Weight gain

Sleep cycles have been ruined, anxiety is rising and many people are falling into an unhealthy lifestyle. I certainly score three-out-of-three on that list.

In recent days I had been hoping to process (curve-fit) the Zoe (citizen science) symptomatics time-series for different regions across the UK, and to write a blog page about the results. However, I have been unable to gain access to the Zoe database. In practice, despite the scheme’s encouraging claims about sharing data or providing access to the ‘deidentified’ data, one is endlessly passed from one database manager to another, or presented with yet another e-form to fill in. The net result is that my 14-day-old application has so far drawn a complete blank.

I had planned to combine Zoe fits with hospital deaths data and so be able to back-calculate the current COVID-19 infection rate, Ro, and the state of regional progression towards ‘herd immunity’. These two key factors are needed for planning the lifting of lockdown. Instead I am reduced to analysing my weight change!

The graph below shows my observations, plus a smooth (empirical) fit, of my weight in 2020. I began by slowly shedding some unwanted bulk (doctor’s orders) in January/February/early March. COVID-19 caused me to begin a stringent (99%) social isolation regime (commencing 6th March). My weight almost immediately started to fall off more rapidly. Official lockdown saw a slight slowing of my weight-loss. (I place the start of lockdown as 23rd March when the UK government banned all “non-essential” travel, shut down almost all businesses, venues, facilities, amenities and places of worship). Unfortunately, in recent days I have started to regain weight.

Time-weight graph. Vertical lines mark dates of personal and official lockdowns. Target weight 82 kg. When, if ever, will I reach my target weight?

In truth, I doubt if any of the wiggles and bumps in the red curve (a lowessLOcally WEighted Scatterplot Smoother) actually have anything to do with lockdown, despite some interesting looking associations. Instead the vacillations illustrate the difficulties of interpreting a purely empirical fit (purely data-driven fit) in comparison with the far better situation of using a model with some underlying physical or physiological basis.

Empiricism vs. physical modelling

To return to the main theme of this series of blog postings – namely applying Hubbert’s maths to COVID-19 time series data – I am always much happier with a model than an empirical fit. This is especially the case when prediction (i.e. extrapolation) is involved. Hubbert based his predictions of peak oil and ultimate resource on a model underpinned by a linearized cumulative logistic equation.

It’s quite sobering to recognise how little is revealed by the weight-change analysis. Without a model it’s almost impossible to judge how my weight will change in the future, or when my target weight might be reached. Mechanistic, or deterministic, modelling is much better than mere empirical fitting. Analytical and deterministic models are to be preferred over empirical models as they are much more general and broader in application. They will often have linear, exponential, or logarithmic ‘backbones’ which can be selected using classic statistical techniques – or as I do with Hubbert through an analysis of variance.

Two articles

In closing. I have been reading two contrasting reports about COVID-19. I found both to be enthralling.

A Greek tragedy

One by the health editor of the Guardian worries, like me, that a second wave, or possibly worse, a long extended tail is in the offing – if the Government continues to treat the virus as a political crisis rather than a medical emergency. Sarah Boseley has won a number of awards for her work on HIV/Aids in Africa. In her article she writes about the views of Robert West, a professor of health psychology at University College London’s Institute of Epidemiology and Health, who sits on the advisory group on behavioural science for Sage. Neither could be exactly classified as a Cummings fan. She writes
“what we now have to recognise is that central government probably cannot be trusted to provide leadership” and furthermore the whole Cummings odyssey “is playing out like a Greek tragedy with the protagonists trapped by their own proclivities to self-destruct – in his case by his hubris and inability to say sorry.”

The end of the affair

The other is by Alistair Haimes who adopts the diametrically opposite point of view. He writes in the Critic “It is the end of the affair. We are no longer at epidemic levels of covid-19 prevalence in the UK … Parents, unions and nervy adults fret about the risk, but there is little need.”

Both articles make fascinating reading.

5 replies to “Glimmer of hope XXII”

  1. Rona Connolly says:

    Haimes is a data processor writing in a magazine co-founded by Hosking, a multi millionaire asset manager who donated a large sum to Vote Leave. I’m guessing the focus there is more on making capital than safeguarding the health of the nation…

  2. thompson says:

    Dear Rona,

    I think you make a very perceptive comment. Another reader has pointed out that my use of the words ‘enthralling’ and ‘fascinating’, in connection with the Haimes piece, was not over helpful. He was left wondering if I approved of the article. I suppose in retrospect I was being deliberately vague.

    PS. Many thanks for the link to the “What Do Countries With The Best Coronavirus Responses Have In Common? Women Leaders” article by Avivah Wittenberg-Cox. I definitely like and approve of Avivah’s article. Bring back Teressa? As another reader pointed out “Theresa May would have handled this better” and “[It] would have suited her better than Brexit“.

  3. Donald McGregor says:

    I’m impressed with your weight loss. Hope you are managing a good fitness regime too.

  4. Roy Thompson says:

    A good fitness regime is more difficult. I have just been loaned a bike to help me get more exercise. Yesterday 100m from home I got a back-wheel puncture. That reminded me of why I recently donated my old bike to the Edinburgh Bike Station. They in turn have set up a scheme to loan or donate bikes to NHS and other COVID-19 workers in Edinburgh and the Lothians. Inevitably over the last few weeks, a number of bike thefts have been reported to police, including three from the Royal Infirmary of Edinburgh where NHS staff have been using bicycles to travel to and from work during the coronavirus pandemic. The three bikes had a combined worth of approximately £4,000. So my old bike is unlikely to have been one of them.

  5. David Stevenson says:

    I can recommend Schwalbe Marathon puncture proof tyres…
    But they’ll make your bike more likely to be stolen…

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