Producer Price Index Manual: Theory and Practice ... - METAC

22. Treatment of Seasonal Products
Figure 22.5 Lowe, Young, Geometric Laspeyres, and Centered Rolling-Year Indices with Imputed
Prices
1.9
1.8
1.7
Index
1.6
1.5
1.4
1.3
Ploi PLOI
Pyi PYI
Pgli PGLI
Pcry P
CRY
1.2
1.1
1
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37
Months
justment. In the following section, the annual basket-type
indices (with and without imputation) defined
earlier in Sections H and I will be seasonally
adjusted using essentially the same method that
was used in Section F and compared with a standard
seasonal adjustment using X-11.
K. Forecasting Rolling-Year Indices
Using Month-to-month Annual
Basket Indices
22.90 Recall that Table 22.23 in Section H presented
the Lowe, Young, geometric Laspeyres (using
carryforward prices), and centered rolling-year
indices for the 37 observations running from December
1970 to December 1973 (P LO , P Y , P GL , and
P CRY , respectively). For each of the first three series,
define a seasonal adjustment factor, SAF, as
the centered rolling-year index P CRY divided by
P LO , P Y , and P GL , respectively, for the first 12 observations.
Now for each of the three series, repeat
these 12 seasonal adjustment factors for observa-
justment. In the following section, the annual basket-type
indices (with and without imputation) defined
earlier in Sections H and I will be seasonally
adjusted using essentially the same method that
was used in Section F and compared with a standard
seasonal adjustment using X-11. tions 13–24
and then repeat them for the remaining observations.
These operations will create three SAF series
for all 37 observations (label them SAF LO , SAF Y ,
and SAF GL , respectively), but only the first 12 observations
in the P LO , P Y , P GL , and P CRY series are
used to create the three SAF series. Finally, define
seasonally adjusted Lowe, Young, and geometric
Laspeyres indices by multiplying each unadjusted
index by the appropriate seasonal adjustment factor:
(22.35) P LOSA ≡ P LO SAF LO ; P YSA
≡ P Y SAF Y ; P GLSA
≡ P GL SAF GL .
585