The David Knights-Whittome Effect

Today’s post follows on from a well researched piece about the Ainger family by project volunteer Clive Orton a few weeks ago.  It is a light-hearted look at an interesting pattern he noticed in the course of his research (can anyone guess that Clive has a background in statistical data?).  But this piece gives a tiny glimpse into just how useful collections like this can be as evidence of patterns and trends in social history, not just locally but across a population.  And from our perspective, it’s just great to have a different take on the items in the collection. I’ll pass over to Clive…

…The David Knights-Whittome Effect: does having your photograph taken make you live longer?

No – of course not! How could that possibly happen? What a stupid idea! That’s what I thought, too, but let’s look at the data. In my work researching people whose images appear in the David Knights-Whittome archive, I have so far looked at the lives of seven ladies. Their life statistics are given below:

DKW_31553_Hillbrook_L

Barbara and Phyllis Hillbrook, with their mother Harriett, Oct 1911

Maria Ainger                      1831-1913 (age 82)

Harriett Hillbrook             1859-1945 (age 85)

Annie Ainger                      1860-1951 (age 90)

Olive Hillbrook                   1896-1981 (age 84/5)

Lena French                       1897-1979 (age 82).

Barbara Hillbrook             1899-1987 (age 88)

Phyllis Hillbrook                1899-1985 (age 85)

 

We can immediately see that all of them lived to well beyond the age of 80, while figures from the Office of National Statistics1 tell us that the average life expectancy for women born in England and Wales between 1891 and 1900 was about 48 years. So all seven exceeded their expected lifespan by a considerably margin. I haven’t calculated the odds of seven women selected at random achieving this feat, but they must be astronomical. Well, that’s it – case made! Never mind how you feel about it, the evidence is incontrovertible. At least for ladies photographed by DKW, that is – we can’t make the same claim for other photographers, and certainly not for men, because so many of them died in WW1.

But is it? Surely such an assault on our common sense demands a deeper examination? Indeed it does. Hidden in the argument is the assumption that our seven ladies are a random sample of all the females living in England and Wales at that time. How reasonable is that? I can think of three reasons why it may not be, and there may be more. First, having a studio portrait taken in the DKW era (1904-1918) set you apart from those who did not – you could afford it. In other words, our ladies are probably better-off than their average contemporaries, and life expectancy is likely to be related to social class and income level. As is still the case today, the better-off you are, the longer you are likely to live. So there is likely to be an effect, but can it account for all the discrepancy we have observed? Probably not, so let’s dig deeper. A second way in which these ladies are set apart is that they all lived in (relatively) salubrious Surrey, so that too might give them an edge in the lifespan stakes. A third point is that some of the ladies are related to each other, and therefore may be argued to share a ‘longevity gene’, for example between the three Hillbrook daughters (including two apparently identical twins) and their mother. But altogether I cannot see these effects accounting for more than a few years’ difference. We still have some way to go.

The most important factor is, I think, the ‘survivor effect’. It’s obvious that all these ladies had lived for long enough to be photographed by DKW. They had already survived the most dangerous years of life (0-5); indeed, Maria had already passed the age of 80 when her photo was taken in 1912. The term ‘life expectancy’ is short for ‘life expectancy at birth’, so we are comparing our ladies against the average for all females, regardless of the age at which they died. But as you get older, the age to which you can expect to live also increases. So what we should be comparing is the age at death of our ladies with the age at death of ladies who also reached the ages at which our ladies were photographed by DKW (and belonging to the same social/geographical class), and that is just not available to me. So the case is not proved, but it’s been a good story and an object-lesson in being careful with data.

  1. English Life Tables no. 17, Office of National Statistics.

    DKW_31553_Hillbrook_L

    Barbara and Phyllis Hillbrook, with their mother Harriett, Oct 1911

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One thought on “The David Knights-Whittome Effect

  1. My wife remembers Olive Hillbrook as founding member of guide movement in Sutton and has memories of practicing putting up bell tents in her back garden in the 1950’s.
    Mike.

    Like

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