“Driving using the rear view mirror” The Dark Art of Population Forecasting Catherine Scott Ross Maconachie Public Health Research Unit West Sussex County Council April 2013

Some simple questions.. How many people with diabetes will live in West Sussex in 2020? If we reduce obesity prevalence by 10% what impact will that have on future need for healthcare? What skills will people need in the future? What will the composition of households be in future? What types of housing will we need in the future? What migration will there be in and out of West Sussex in future?

‘The first Baby Boomer has come to collect Social Security, how cute….’

‘As you can see, by late next month you’ll have over four dozen husbands. Better get a bulk rate on wedding cake.’

Past population projections Source: ONS

Now let’s look at some (incorrect as based on rates derived from previous MYEs) projections!

WSx Population key areas are:- 1.50% more people aged Huge expansion in number people aged Growth in upper working age - consider 2031! 4.Contraction of key carer groups to support This corresponds to an 25% increase in 65+, a 31% increase in 85+ and an old age dependency ratio increase of 19%

MIGRATION

Sensitivity analysis - the effect of fertility, mortality and aggregate migration

Cautionary tale 1 ‘It will be years - not in my time - before a woman will become Prime Minister’ Margaret Thatcher, future Prime Minister, October 26th, 1969.

Cautionary tale 2 ‘Earlier on today, apparently, a woman rang the BBC and said she heard there was a hurricane on the way... well, if you're watching, don't worry, there isn't!’ Michael Fish, weather forecaster, a few hours before the worst storm since 1703 hit South East England in October 1987

Weather forecast for Crawley last week on Met Office website There is a 20% chance of precipitation on Thursday

Chart 5.1 GDP projection based on market interest rate expectations The fan chart depicts the probability of various outcomes for GDP growth. To the left of the first vertical dashed line, the distribution reflects the likelihood of revisions to the data over the past; to the right, it reflects uncertainty over the evolution of GDP growth in the future. If economic circumstances identical to today’s were to prevail on 100 occasions, the MPC’s best collective judgement is that the mature estimate of GDP would lie within the darkest central band on only 10 of those occasions. The fan chart is constructed so that outturns are also expected to lie within each pair of the lighter green areas on ten occasions. Consequently, GDP growth is expected to lie somewhere within the entire fan on 90 out of 100 occasions. The bands widen as the time horizon is extended, indicating the increasing uncertainty about outcomes. See the box on page 39 for a fuller description of the fan chart and what it represents. The second dashed line is drawn at the two-year point of the projection.

The effective of housing assumptions – various scenarios ONS +5% ONS Housing YoungFam Housing Oldfam WSCC Model Natural Change Natural Change -5%

Cautionary tale 3 ‘They couldn't hit an elephant at this dist- ‘ Last words of Gen. John Sedgwick, spoken as he looked out over the parapet at enemy lines during the Battle of Spotsylvania in 1864.

Cautionary tale 4 ‘There is not the slightest indication that nuclear energy will ever be obtainable. It would mean that the atom would have to be shattered at will’ Albert Einstein, 1932

Key messages Vital to have best population data possible Implications of different structures need to be understood by policy makers Dependency ratio an important statistic in the south east Key drivers of migration are jobs and housing, both can be influenced