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From (Benigno, 2022) I have an index called Global Supply Chain Pressure Index (GSCPI) provided at the end of the post. The index was shared at monthly frequency.

A part of the data provided is as below

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Now I want the annual data, for example, the GSCPI of year 1998 and 1999. Could you please tell me what I should do in such a case?

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    $\begingroup$ Seems the index is normalized such that a zero indicates that the index is at its average value with positive (negative) valued representing how many standard deviations the index is above (below) this average value. Insofar, I am not sure how one would interpret an annual value (ie.g. it's not a flow). What would you need this for? $\endgroup$
    – Alex
    Aug 18, 2022 at 7:02
  • $\begingroup$ @Alex because other variables are at annual frequency $\endgroup$ Aug 18, 2022 at 7:03
  • $\begingroup$ If it's just end of year GDP or the like, I think it's valid to just use and of year (DEC) of the index. It literally just shows the SD from average (at any point in time that is reported). $\endgroup$
    – Alex
    Aug 18, 2022 at 7:05
  • $\begingroup$ @Alex , so you mean the index GSCPI for 1998 is -0.56 and 1999 is -0.02 if I understand you correctly? $\endgroup$ Aug 18, 2022 at 7:22
  • $\begingroup$ @PhilNguyen: for what purpose do you need the annual aggregation? $\endgroup$
    – BrsG
    Aug 18, 2022 at 7:46

1 Answer 1

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Indices are typically aggregated to a lower frequency by taking the average over the sub-periods (the 12 months of the year in your case) if it's just to represent the data in that lower frequency.

However, if it's for further analysis, more custom aggregations might be more appropriate and would very much depend on the exact purpose. For example, if you were looking at the impact on inflation, which, let's assume, materialises with a lag of six months, you may want to check whether the average over 1998M7-1999M6 would be a better choice. Or, for example, if it's about the impact of supply chain security, you may want to take the standard deviation over a year or some related measure.

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