How to model demography

This guide walks through building demographic projections: starting from the baseline, experimenting with assumptions, and saving or sharing your scenarios. For the full reference of every table, input and output, see the demographic data model.

1. Start from the baseline

Pick a country at the top. The tool opens with a baseline configuration — the official statistics office’s data and assumptions. For Spain the migration preset scenarios (INE Central / High / Low) reproduce the official INE 2024–2074 population projection; combined with the INE population, fertility and HMD mortality (with the default mortality improvement), the baseline tracks the national forecast rather than an arbitrary guess.

So the very first Add scenario gives you a credible reference line.

2. Experiment with the assumptions

Everything is editable — this is the point of the tool:

• Change the projection period (start year, number of years).
• Swap the population / fertility / mortality / migration data set.
• Pick a different migration preset (Central / High / Low), or
• Add a fine-tuning trend to fertility, mortality or migration: ±X% per year for N years, then plateau (e.g. mortality improving faster, fertility recovering, migration tapering).

Preview any assumption before running with Show projections: see the age curve, where a trend takes it by the horizon (dotted), and the “was → became” summary — life expectancy for mortality, TFR for fertility, net total for migration. For migration switch to Total by year to see the whole path.

3. Build a fan of forecasts

Give the run a Scenario name and click Add scenario. Each run adds a line to the chart, so you accumulate a fan of forecasts — e.g. a low, central and high variant — on one axis, with a table of their assumptions below. Use the checkboxes in the Scenarios list to show/hide lines, Load to pull a scenario’s settings back into the form to tweak, or Del to remove it.

The Outputs tab turns any scenario into a population pyramid (animated or two-year compare) and cohort trends (16–64, 65+, custom), with CSV export. The History tab shows the historical mortality, life expectancy and (for Spain) healthy life expectancy behind the country — and can overlay your projected life expectancy on the historical curve.

4. Save and share

Sign in (Google / LinkedIn) to Save a scenario to My Reports, kept indefinitely. From My Reports, Share publishes it and copies a public link (/s/…) that anyone can open read-only, no sign-in required. (Sharing currently covers one scenario per report.) Anonymous work lives in your browser and migrates to your account when you sign up.