Most published economic indices are revised after they are first published—information does not come in all at once, and timely publication dictates that the preliminary index numbers be later revised. The repeated-measures indices developed in the preceding chapters are vulnerable to revisions after especially long intervals of time, since they have the property that, unless the repeated measures come sequentially (which they do not necessarily), there will be revisions in the indices after the index numbers are first produced, even if the raw data used then were perfectly accurate and complete. There are other index number construction methods, such as ordinary-least-squares regression-per-period hedonic regressions, that do not normally produce revisions; this would at first seem to be an advantage, but an index number construction method that does not produce revisions is not a virtue if new information tends to arrive that implies revisions and is just ignored. This chapter addresses the whole problem of index number revisions in the following sections: Variance components in regression-per-period hedonics; Interval-linked indices; Indices that are derived by conditioning on lagged index values. The final section of the chapter draws some sort of interpretation of what has gone before.
Keywords: conditioning on lagged index values, economic indices, index number construction, index number revision, index numbers, Interval-linked indices, lagged index values, ordinary-least-squares regression-per-period hedonic regressions, regression-per-period hedonics, repeated-measures indices, Variance components