A forecast in ten minutes: the canonical QPM in qpmR

In qpmR: Quarterly Projection Models for Monetary Policy Analysis

knitr::opts_chunk$set(collapse = TRUE, comment = "#>",
                      fig.width = 7, fig.height = 5)

qpmR implements the class of semi-structural quarterly projection models (QPM) used in central-bank Forecasting and Policy Analysis Systems: an IS curve, a hybrid Phillips curve, a forward-looking inflation-targeting rule, and an exchange-rate block, solved under model-consistent expectations.

The canonical model

qpm_template("bkl") ships the canonical Berg–Karam–Laxton (IMF WP/06/80–81) small open economy model with an illustrative emerging-economy calibration — a 5 percent inflation target and a positive country risk premium.

library(qpmR)
m <- qpm_template("bkl")
m

The policy rule responds to expected year-on-year inflation four quarters ahead, E(pi4[+4]); the four-quarter identity uses lags back to pi[-3]. qpmR turns those long leads and lags into auxiliary states automatically when the model is solved.

Solving and checking

sol <- qpm_solve(m)
sol

The Blanchard–Kahn line is a real diagnostic: an indeterminate or explosive model refuses to solve and the error names the usual economic cause. Violating the Taylor principle, for instance:

qpm_solve(qpm_calibrate(m, c2 = -0.5))

Monetary transmission

ir <- irf(sol, shock = "eps_i", horizon = 16)
ir
plot(ir, vars = c("i", "r", "pi", "y_gap", "q", "pi4"))

A policy tightening raises the real rate, opens a negative output gap, appreciates the currency on impact (UIP), and produces the hump-shaped disinflation with a mild rebound as policy later eases below neutral — the standard QPM transmission story.

History and forecast

Until the Kalman filter arrives in 0.2, initial states come from simulation:

histq <- simulate(sol, nsim = 48, seed = 7, burn = 20)
fc <- qpm_forecast(sol, from = histq, horizon = 12)
fc
plot(fc, vars = c("pi", "i", "y_gap", "q"))

The fan bands are analytic, from the forecast-error variance recursion V_h = P V_{h-1} P' + Q S Q'.

Specification checks

qpm_lint(m)

Adapting the model to your country

Real engagements never use the canonical model unchanged. Extension blocks make that adaptation reusable and reviewable instead of a fork.

The most common adaptation is disaggregating the CPI. Food is 30-50 percent of the basket across most of sub-Saharan Africa and South Asia, and a single-inflation model cannot represent the policy question there -- supply shocks to food dominate headline, but policy should look through the relative-price component:

m_food <- add_block(qpm_template("bkl"), block_food_cpi(weight = 0.45))
plot(irf(qpm_solve(m_food), shock = "eps_pifood", horizon = 16),
     vars = c("pi_food", "pi", "pi_core", "i"))

Food inflation jumps, headline follows scaled by the basket weight, and core barely moves -- so the policy response stays small. That is the model saying what a good desk would say.

Exchange-rate management is the other common adaptation. One intensity argument spans the regimes: zero reproduces the free float exactly, larger values approach a peg.

peak_q <- function(m) {
  ir <- irf(qpm_solve(m), shock = "eps_prem", horizon = 12, size = 1)
  max(abs(ir$value[ir$variable == "q"]))
}
c(float   = peak_q(qpm_template("bkl")),
  managed = peak_q(add_block(qpm_template("bkl"), block_fx_intervention(1))),
  peg     = peak_q(add_block(qpm_template("bkl"), block_fx_intervention(4))))

Whatever a country team changes, qpm_diff() makes it reviewable:

qpm_diff(qpm_template("bkl"), m_food)

Real data: Czechia

qpmR ships czechia, a quarterly dataset from 1996 in the model's units (see ?czechia). With trends = "rw" the equilibrium real exchange rate and potential growth become random walks — the model then has unit roots and qpm_filter() switches to diffuse initialization automatically.

mcz <- qpm_calibrate(qpm_template("bkl", trends = "rw"),
                     pi_tar = 2, istar_ss = 2, pistar_ss = 2,
                     prem_ss = 1, a5 = 0.4)
cz <- czechia[czechia$period >= "1999",
              c("period", "pi4", "i", "q", "dy_obs", "istar", "pistar")]
fit <- qpm_filter(mcz, cz)
fit

The smoothed latent states reproduce the known history — the pre-GFC boom, the 2009 and 2013 recessions, the COVID crater, the trend real appreciation of the koruna, and the post-GFC fall in potential growth:

plot(fit, vars = c("y_gap", "dy_bar", "r_bar", "q_gap"))

Historical shock decomposition of the 2021-23 inflation wave:

dec <- qpm_decompose(fit)
plot(dec, var = "pi4", periods = (fit$n_obs - 33):fit$n_obs)

And a forecast from the smoothed end-of-sample state:

fc <- qpm_forecast(qpm_solve(mcz), from = fit, horizon = 12)
plot(fc, vars = c("pi4", "i", "y_gap", "q"))

Note the honesty of the diagnostics on real data: the Ljung-Box test flags autocorrelated exchange-rate innovations (the driftless q_bar random walk absorbs the appreciation trend through its shocks), and the 2022-23 inflation surprises show up as large outliers. That is the model asking for judgment and recalibration — which is what 0.3 is for.

Policy analysis: conditions, judgment, rounds

A forecast becomes policy analysis when you can impose assumptions on it. qpm_condition() inverts the model for the shocks behind any assumed path -- with an explicit anticipated switch, because an announced rate path and a sequence of surprises are different economics:

base <- qpm_forecast(qpm_solve(mcz), from = fit, horizon = 12)
hold <- qpm_condition(base,
                      i = stats::setNames(rep(3.5, 4), base$periods[1:4]),
                      anticipated = TRUE, instruments = "eps_i")
hold

Judgment is a logged, auditable operation rather than a spreadsheet tweak:

judged <- add_judgment(base, pi4 = stats::setNames(0.4, base$periods[3]),
                       author = "prices desk",
                       rationale = "announced energy-tariff increase")
judgment_log(judged)

A forecast round archives the whole pipeline -- model, calibration, data vintage, filtration, conditioned forecast -- as one replayable object, and compare_rounds() answers the question every chief economist asks: why did the forecast move?

czA <- cz[cz$period <= "2025-Q4", ]
rA <- qpm_round("2026-Q1 March", mcz, czA, horizon = 12)
rB <- qpm_round("2026-Q3 September", mcz, cz, horizon = 12)
rB <- add_judgment(rB, pi4 = c("2027-Q1" = 0.4), author = "prices desk",
                   rationale = "announced energy-tariff increase")
rev <- compare_rounds(rA, rB, variables = c("pi4", "i", "y_gap"))
print(rev, variables = "pi4", periods = "2027-Q1")
plot(rev, variable = "pi4")

The contributions telescope, so they sum to the total revision exactly, and the decomposition endpoints are verified against the archived rounds. save_round() / load_round() / list_rounds() manage the on-disk round store, with human-readable CSV sidecars for auditing without R.

Closing the round: audit and report

An archived round is only useful if it still reproduces. verify_round() re-runs the whole pipeline from the round's own contents — model, calibration, data vintage, conditions and judgment — and checks the published numbers against the archive:

verify_round(rB)

A round that no longer reproduces is a finding, not a mystery: the report names the largest deviation, the variables responsible, and any qpmR version drift. Loaded from a store, it also checks the CSV sidecars against the object, so a hand-edited audit trail shows up.

The round then becomes the deliverables a policy meeting runs on — the standard chart pack and the monetary policy report, which carries the executive summary, the fan charts, the gaps, the shock decomposition, the judgment ledger and the revision against the previous round:

chart_pack(rB, "chart_pack.pdf")
qpm_report(rB, "mpr.html", compare_to = rA)

qpm_report() always writes the .Rmd source next to its output, on the principle that institutions replace the template's text, not its plumbing.

Where to go next

Estimation — priors, posterior sampling on the filter likelihood, identification diagnostics, marginal likelihoods, and posterior fan charts — is covered in vignette("qpmR-estimation"). The policy experiments build on the same objects: qpm_rule_eval() scores alternative rules on the inflation-output variability frontier, qpm_counterfactual() replays history with shocks switched off, qpm_compare_models() sets two models' impulse responses and moments side by side, and fevd() and model_properties() report which shocks drive which variables. write_dynare() exports any model as a .mod file for an independent check in Dynare.

qpmR documentation built on Sept. 29, 2026, 5:10 p.m.