23 Feb
2004
23 Feb
'04
2:24 p.m.
On Mon, 23 Feb 2004, Hillsman, Ed wrote:
The following question was referred to me for comment
and help, and I don't
recall seeing any discussion of this on the CTPP listserver. If you have any
thoughts on this, I will pass them along to the questioner. Thanks in
advance for any insight you may have.
Ed Hillsman
Its been discussed on the SDC-L list. Here is a useful reply:
Date: Fri, 13 Feb 2004 07:11:52 -0500
From: phillip.a.salopek(a)CENSUS.GOV
Subject: Re: Question on trend in average commute time
I do not think the differences in average travel time you are seeing
between Census 2000 and ACS reflect changes that have actually occurred.
The avg. travel times reported in ACS have been lower than in Census
2000
across the board right from the start. If you look at
the distributions
of
travel time you'll see that in ACS people report a
higher proportion of
short trips (less than 20 mins.) and a lower frequency of long trips (60
mins. plus) than were reported in the census. The bottom line here is
that
while there are many similarities between the two
surveys, there are
also
some differences. However, we can't point to a
specific reason and say
this
is why the numbers differ. Ultimately, they are
different surveys that
are
producing slightly different results.
--Phillip Salopek
Chief, Journey to Work and Migration Statistics Branch
Population Division
Jim Bash
CAGIS, Geography & Anthropology, UIC