Please, no more projections. What we need are predictions, and they’re harder

Please, no more projections. What we need are predictions, and they’re harder
Staff reporterNovember 19, 2019

GUEST OBSERVATION

It is difficult to make predictions, especially about the future. (attributed to Danish physicist Niels Bohr)

The difficulty of making predictions has long been known, but the rise of the internet means that it is getting harder to hide the gaps between predictions and reality.

Perhaps the most significant example of repeated failed projections has been the International Energy Agency’s projections of the importance of renewable power – the proportion of electricity generated by solar and wind and other renewable sources other than hydro.

Beginning in 1994, when generation from these sources was negligible, the Agency has produced estimates of the future share of renewables every two years.

Every two years, with striking regularity, the previous estimates have been exceeded (hugely) and the new set has been revised upwards. But never by enough. Each time the upward revision has been inadequate.

This graph, prepared by Paul Mainwood from IEA reports, illustrates the point:

Projections versus reality

Reality versus repeated projections of renewables share of electricity generation (ex hydro). Paul Mainwood, Quora

The dashed lines represent successive projections from 1994 to 2016.

The solid red line represents the actual growth of non-hydro renewables as a share of total electricity generation.

What can be seen is that eleven times in a row the projected growth in renewables was far too low and had to be upgraded. Eleven times in a row the upgrades weren’t big enough.

As a joke (indicated by the green line) Mainwood “corrected” the 2016 projection for the typical under-projection:

Projections plus “corrected” 2016 projection

Reality versus projections of renewables share of electricity generation (ex hydro) plus 2016 projection corrected for typical undershoot. Paul Mainwood

Projections often understate change

Another striking example relates to religious belief. In 2015 the Pew Research Institute released a report suggesting a gradual decline in Christianity in the United States.

The headline finding for the US:

"Christians will decline from more than three-quarters (75%) of the population in 2010 to two-thirds (66%) in 2050."

Yet only four years later in 2019, Pew released another report with this headline finding about the US:

'In 2018 and 2019, 65% of American adults describe themselves as Christians when asked about their religion, down 12 percentage points over the past decade."

Thus, a decline expected to take forty years had taken place inside ten.

Moreover, Christian affiliation is highest in the older age cohorts, very few members of which will be around in 2050. Looking at the younger cohort born after 1981, only 49% claim a Christian affiliation, a proportion that has declined by 16 percentage points in a decade. Unless that trend is rapidly reversed, or later cohorts experience a religious revival, Christians will be a minority well before 2050.

They enable modellers to escape responsiblity

Faced with outcomes of this kind, modellers often defend themselves by drawing a distinction between “predictions” and “projections”.

A prediction (Latin for “foretelling”) is a claim about what is most likely to happen in the future. By contrast, a projection (“casting forward”) is a model output derived by extrapolating past trends, holding some parameters constant and allowing others to vary.

The International Energy Agency projections were characterised by the assumption that the costs of renewable energy would change only slowly, rather than continuing the extraordinary decline that began in the 1970s.

In the case of the Pew projections, the crucial parameter is conversion rates – the frequency with which people brought up with one religion (including “no religion”) change to another. The Pew projections were based on the assumption conversion rates will remain unchanged.

It is the opposite of the widely-held but controversial “secularisation hypothesis” which states that modernisation leads to increased conversions to “no religion”.

Predictions force them to take responsibility

Projections are useful in the development of models. All models are based on past experience and have to assume that in some respects the future will be like the past. By examining the projections generated under particular assumptions about which variables and parameters will remain constant, it is possible to understand how models works and make modelling choices.

But projections of this kind are of no use in informing people not familiar with the material. They mislead casual readers of the Australia’s budget.

The budget uses both predictions and projections.

For the two years following each budget the Commonwealth uses “forecasts” which it is prepared to stand by, then for the next two it presents mechanical “projections”:

2019-20 Commonwealth budget, Budget Paper 1

When asked to defend (for example) its wage growth number of 3½%, the treasury points out that it is a mechanical projection rather than a forecast, a distinction lost on all but the most enthusiastic of budget devotees.

In practice it is impossible to separate the two.

Even though both the International Energy Association and Pew describe their estimates as “projections” they are almost invariably treated as predictions. 

Since any statement about the future will be treated as a prediction, the only serious option for modellers prepared to be truthful with the public is to bite the bullet and make predictions.

It means working hard to make the best possible estimate of the future paths of all model parameters, and using judgement to take account of everything else.

It’s what those of us looking to experts for guidance deserve.The Conversation

John Quiggin, Professor, School of Economics, The University of Queensland.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Editor's Picks

First look: MADE Property doubles down in Kirribilli new apartment market
Spyre Group brings successful Queensland blueprint to Melbourne with Hampton Ltd
Saxon Street by Milieu to bring new housing and urban design to Brunswick’s cultural core
Construction begins at Fishermans Bend Innovation Precinct
Gurner reveals new plans for final Jam Factory stage

Related Projects

16-22 Maud Street, Newstead QLD 4006
16-22 Maud Street, Newstead QLD 4006
16-22 Maud Street, Newstead QLD 4006
Price
Contact agent
35-37 Mount Street, Prahran VIC 3181
35-37 Mount Street, Prahran VIC 3181
35-37 Mount Street, Prahran VIC 3181
Price
Contact agent
118-124 Benelong Road, Cremorne NSW 2090
118-124 Benelong Road, Cremorne NSW 2090
118-124 Benelong Road, Cremorne NSW 2090
Price
Contact agent
118-120 Matthew Flinders Drive, Cooee Bay QLD 4703
118-120 Matthew Flinders Drive, Cooee Bay QLD 4703
118-120 Matthew Flinders Drive, Cooee Bay QLD 4703
Price
Contact agent
26-62 Kinross Road, Thornlands QLD 4164
26-62 Kinross Road, Thornlands QLD 4164
26-62 Kinross Road, Thornlands QLD 4164
Price
Contact agent
9-11 Baroonba Street, Whitebridge NSW 2290
9-11 Baroonba Street, Whitebridge NSW 2290
9-11 Baroonba Street, Whitebridge NSW 2290
Price
Contact agent
18 Ransley Street, Penrith NSW 2750
Perle, East Side Quarter, Penrith - 18 Ransley Street, Penrith
18 Ransley Street, Penrith NSW 2750
Price
Contact agent
Ernest Cavanagh Street, Gungahlin ACT 2912
Raya, Gungahlin - Ernest Cavanagh Street, Gungahlin
Ernest Cavanagh Street, Gungahlin ACT 2912
Price
Contact agent
39 Browning Street, South Brisbane QLD 4101
39-41 Browning Street, South Brisbane - 39 Browning Street, South Brisbane
39 Browning Street, South Brisbane QLD 4101
Price
Contact agent
675 Gardeners Road, Mascot NSW 2020
Kiara North, Mascot - 675 Gardeners Road, Mascot
675 Gardeners Road, Mascot NSW 2020
Price
Contact agent
187 Salvado Road, Jolimont WA 6014
Jolie, Jolimont - 187 Salvado Road, Jolimont
187 Salvado Road, Jolimont WA 6014
Price
Contact agent
47 Maning Avenue, Sandy Bay TAS 7005
Grace Residences - 47 Maning Avenue, Sandy Bay
47 Maning Avenue, Sandy Bay TAS 7005
Price
Contact agent
Cove Lane, Narooma NSW 2546
Cove, Narooma - Cove Lane, Narooma
Cove Lane, Narooma NSW 2546
Price
Contact agent
52-56 Ramsay Street, Five Dock NSW 2046
Ava, Five Dock - 52-56 Ramsay Street, Five Dock
52-56 Ramsay Street, Five Dock NSW 2046
Price
Contact agent
2375 Gold Coast Highway, Mermaid Beach QLD 4218
The Alfred - 2375 Gold Coast Highway, Mermaid Beach
2375 Gold Coast Highway, Mermaid Beach QLD 4218
Price
Contact agent
129-131 Russell Ave, Dolls Point NSW 2219
ALLURE COLLECTION - 129-131 Russell Ave, Dolls Point
129-131 Russell Ave, Dolls Point NSW 2219
Price
Contact agent
62 Constitution Avenue, Parkes ACT 2600
The Eastbourne on Commonwealth Park - 62 Constitution Avenue, Parkes
62 Constitution Avenue, Parkes ACT 2600
Price
Contact agent
155 Old Burleigh Road, Broadbeach QLD 4218
Sandpiper, Broadbeach - 155 Old Burleigh Road, Broadbeach
155 Old Burleigh Road, Broadbeach QLD 4218
Price
Contact agent
33 Vulture Street, West End QLD 4101
33 Vulture Street, West End QLD 4101
33 Vulture Street, West End QLD 4101
Price
Contact agent
19 Governor Terrace, Murarrie QLD 4172
Park Hill Village Collection, Murarrie - 19 Governor Terrace, Murarrie
19 Governor Terrace, Murarrie QLD 4172
Price
Contact agent
122 Marine Parade, Miami QLD 4220
Nalu, Miami - 122 Marine Parade, Miami
122 Marine Parade, Miami QLD 4220
Price
Contact agent
34 Jacaranda Place, Indooroopilly QLD 4068
34 Jacaranda Place, Indooroopilly QLD 4068
34 Jacaranda Place, Indooroopilly QLD 4068
Price
Contact agent
167 Old Burleigh Road, Broadbeach QLD 4218
167 Old Burleigh Road, Broadbeach QLD 4218
167 Old Burleigh Road, Broadbeach QLD 4218
Price
Contact agent
21 Queens Way, Yeerongpilly QLD 4105
Yeerongpilly Green - 21 Queens Way, Yeerongpilly
21 Queens Way, Yeerongpilly QLD 4105
Price
Contact agent
445-449 River St, Ballina NSW 2478
Solhaven - 445-449 River St, Ballina
445-449 River St, Ballina NSW 2478
Price
Contact agent
52 Sunset Boulevard, Surfers Paradise QLD 4217
52 Sunset Boulevard, Surfers Paradise QLD 4217
52 Sunset Boulevard, Surfers Paradise QLD 4217
Price
Contact agent
6 Jack Brabham Drive, Hurstville NSW
Horizon Hurstville - 6 Jack Brabham Drive, Hurstville
6 Jack Brabham Drive, Hurstville NSW
Price
Contact agent
49 Seena Drive, Edgeworth NSW 2285
49 Seena Drive, Edgeworth NSW 2285
49 Seena Drive, Edgeworth NSW 2285
Price
Contact agent
Lot 118 Ocean Steamers Road, Port Adelaide SA 5015
Lot 118 Ocean Steamers Road, Port Adelaide SA 5015
Lot 118 Ocean Steamers Road, Port Adelaide SA 5015
Price
Contact agent
203 Ashmore Road, Benowa QLD 4217
203 Ashmore Road, Benowa QLD 4217
203 Ashmore Road, Benowa QLD 4217
Price
Contact agent
774 Ripley Road, Ripley QLD 4306
774 Ripley Road, Ripley QLD 4306
774 Ripley Road, Ripley QLD 4306
Price
Contact agent
6 Homelea Court, Rivervale WA 6103
6 Homelea Court, Rivervale WA 6103
6 Homelea Court, Rivervale WA 6103
Price
Contact agent
7002 Ripley Road, Ripley QLD 4306
7002 Ripley Road, Ripley QLD 4306
7002 Ripley Road, Ripley QLD 4306
Price
Contact agent
3 Delos Way, Sorrento WA 6020
3 Delos Way, Sorrento WA 6020
3 Delos Way, Sorrento WA 6020
Price
Contact agent
77 Sutton Street, Redcliffe QLD 4020
77 Sutton Street, Redcliffe QLD 4020
77 Sutton Street, Redcliffe QLD 4020
Price
Contact agent
119 Queen Street & 86 King Street, Bendigo VIC 3550
119 Queen Street & 86 King Street, Bendigo VIC 3550
119 Queen Street & 86 King Street, Bendigo VIC 3550
Price
Contact agent
181 Prospect Road, Prospect SA 5082
181 Prospect Road, Prospect SA 5082
181 Prospect Road, Prospect SA 5082
Price
Contact agent
593-595 Albany Highway, Victoria Park WA 6100
593-595 Albany Highway, Victoria Park WA 6100
593-595 Albany Highway, Victoria Park WA 6100
Price
Contact agent
1-28, 40 Civic Way, Rouse Hill NSW 2155
1-28, 40 Civic Way, Rouse Hill NSW 2155
1-28, 40 Civic Way, Rouse Hill NSW 2155
Price
Contact agent
93-97 Bay Street, Brighton VIC 3186
93-97 Bay Street, Brighton VIC 3186
93-97 Bay Street, Brighton VIC 3186
Price
Contact agent
22-38 & 27-31 The Avenue, Coburg VIC 3058
22-38 & 27-31 The Avenue, Coburg VIC 3058
22-38 & 27-31 The Avenue, Coburg VIC 3058
Price
Contact agent
1F Ashline Street, Wollert VIC 3750
1F Ashline Street, Wollert VIC 3750
1F Ashline Street, Wollert VIC 3750
Price
Contact agent
Lots 100 & 900 Kentucky Court, Cockburn Central WA 6164
Lots 100 & 900 Kentucky Court, Cockburn Central WA 6164
Lots 100 & 900 Kentucky Court, Cockburn Central WA 6164
Price
Contact agent
1260-1272 Malvern Road, Malvern VIC 3144
1260-1272 Malvern Road, Malvern VIC 3144
1260-1272 Malvern Road, Malvern VIC 3144
Price
Contact agent
472 Regency Road, Prospect SA 5082
472 Regency Road, Prospect SA 5082
472 Regency Road, Prospect SA 5082
Price
Contact agent
273A Gorge Road, Paradise SA 5075
273 Gorge Road, Paradise SA 5075 - 273A Gorge Road, Paradise
273A Gorge Road, Paradise SA 5075
Price
Contact agent
270 The Esplanade, Miami QLD 4220
270 The Esplanade, Miami QLD 4220
270 The Esplanade, Miami QLD 4220
Price
Contact agent
2 & 6 Austral Parade, East Bunbury WA 6230
2 & 6 Austral Parade, East Bunbury WA 6230
2 & 6 Austral Parade, East Bunbury WA 6230
Price
Contact agent
5 Charles Street, Charlestown NSW 2290
5 Charles Street, Charlestown NSW 2290
5 Charles Street, Charlestown NSW 2290
Price
Contact agent
59 & 69 Merthyr Road, New Farm QLD 4005
59 & 69 Merthyr Road, New Farm QLD 4005
59 & 69 Merthyr Road, New Farm QLD 4005
Price
Contact agent