wave_step() reports the level of its own period and the net change against each carry it
was given – that is, pairwise contrasts. Many published series are not pairwise: a
rolling quarter is the average of three consecutive months, a semester-on-semester contrast
is c(-1/2, -1/2, 1/2, 1/2), an annual average is rep(1/W, W). wave_contrast() estimates
any such combination \(\psi = a'\theta\) directly from the carries the chain already wrote
to disk, with \(V(\psi) = a' \Sigma a\).
Arguments
- carries
a list of
wf_wave_carryobjects, one per period entering the combination. Order defines the order ofcontrast; they are used as given (not sorted).- estimand
name of the estimand to combine, as it appears in
carry$point(a domain estimand is named e.g."rate|sex=F").- contrast
numeric weights, one per carry. Defaults to the average
rep(1/W, W).- level
confidence level for the interval.
Value
a one-row data.frame with estimate, se, V, lo, hi, R_used, the periods
and the contrast used, plus the covariance matrix Sigma as an attribute.
Details
The carries make this possible without keeping the waves in memory: each one stores the R
replicate values of every declared estimand, and those replicates are paired across
periods because the coordination transferred the PSU multiplicities. Stacking them into an
R x W matrix and taking its (uncentred-at-R) covariance recovers the full between-period
covariance matrix, from which any linear combination follows. With contrast = c(-1, 1) the
result reproduces the $change row of wave_step() exactly.
See also
wave_step(), wave_carry(); panel_estimate() does the same on a
wave_bootstrap() object, when all waves are held together.