#109 Another X-12 Issue

closed-invalid
None
5
2009-06-30
2009-06-30
Greg K
No

In attempting to seasonally adjust labor force data from the Nassau-Suffolk metro area, I'm getting an output that does not look at all like it is seasonally adjusted. There is no error message, and data comes out. However, the original and "adjusted" series look almost identical.

The gretl file is attached.

gretl 1.8.1 on Windows XP

Discussion

  • Allin Cottrell
    Allin Cottrell
    2009-06-30

    There's no bug here. The variation in your series is not seasonal.
    Try a regression with a time trend, a dummy for around 1995, and
    an interaction between dummy and trend (all this to capture the
    initial fall and subsequent trend rise). Now add monthly dummies
    and test them for significance: they're not in the least significant.

     
  • Allin Cottrell
    Allin Cottrell
    2009-06-30

    • assigned_to: nobody --> allin
    • status: open --> closed-invalid
     
  • Allin Cottrell
    Allin Cottrell
    2009-06-30

    If you look at the spectrum of your series, detrended, you'll see the
    peaks are at about 13 months, 6.5 months and 4.3 months. It's not
    an annual pattern.

     
  • Allin Cottrell
    Allin Cottrell
    2009-07-01

    OK, my last comment. I suspect a bug in your data source. You have
    what looks very much like a seasonal cycle (overlaid on a broken
    trend), yet the cycle is not seasonal according to all the statistics:
    the periodicity is wrong. Is it possible that that data source in fact
    has thirteen values per year, one an annual average?

     
  • Allin Cottrell
    Allin Cottrell
    2009-07-01

    OK, I lied about that being my last comment. I have confirmed my
    suspicion. Every 13th observation is an annual average. You have
    to pay attention to this sort of thing! To fix this in gretl:

    genr time
    genr month = time%13
    smpl month!=0 --restrict
    setobs 12 1990:01 --time-series

    Then save the corrected data.