On Tue, 4 Jan 2022, Erin Stearns wrote:
Hello R-sig-Geo friends & happy 2022!
Running EBlocal() on US county sf dataset and getting NaN values where
Empirical Bayes and a BYM model are returning values and I do not
understand why. Additionally, does anyone know how to examine the parameters
attribute list from the output of the EBlocal() function? I have not been
able to look at this and perhaps that would be informative.
Yes, you are right:
summary(attr(seb_icu, "parameters")$a)
summary(attr(seb_icu, "parameters")$m)
which(attr(seb_icu, "parameters")$a == 0 &
attr(seb_icu, "parameters")$m == 0)
which(is.nan(seb_icu$est))
showing that the NaNs are caused by a division by zero:
est <- m.i + (xi - m.i) * (a.i / (a.i + (m.i/ni)))
In fact, if m.i and C.i (see Marshall's paper) are both zero, a.i becomes
zero, and leads to the division by zero. The underlying reason is that
Marshall never tested a setting where many ri are zero, so the count of
cases in a small neighbourhood of neighbouring counties was almost never
zero:
table(thedata$icu_bed_avg == 0)
FALSE TRUE
1437 1783
Had tests been done on > 50% cases, the problem would have been detected,
but probably not resolved, as the issue is with entitation - .
The same counties have NaNs if those with no neighbours are dropped (less
the no-neighbour counties), so this is not caused by assuming that the
lagged value of an entity with no neighbours is zero.
To get closer to the original paper, probably counties should be
aggregated to reduce the number with no cases, and so meet the underlying
assumptions.
Hope this helps,
Roger
*Function call:*
seb_icu <- EBlocal(thedata$icu_bed_avg, thedata$over18pop, nb = nb,
zero.policy = TRUE)
*Environment details:*
OS: Windows 10 x64
R Version: 4.1.1
spdep version: 1.1-11
sf version : 1.0-3
Full dataset and code to reproduce can be found for download here.
<https://eur02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fapp.box.com%2Fs%2Fr26ta0gl9avwlwm65ivtze7j97hyw8i7&data=04%7C01%7CRoger.Bivand%40nhh.no%7Ca717ef6fd6574eb6a40a08d9cfa5d91d%7C33a15b2f849941998d56f20b5aa91af2%7C0%7C0%7C637769134198352241%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C2000&sdata=LJEJ3SgKe0wEzD21Re3%2B4Jfl5LpSD6SpDFYPzsFP7HE%3D&reserved=0>
Thank you in advance for your help!
Best,
Erin
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--
Roger Bivand
Emeritus Professor
Department of Economics, Norwegian School of Economics,
Postboks 3490 Ytre Sandviken, 5045 Bergen, Norway.
e-mail: roger.biv...@nhh.no
https://orcid.org/0000-0003-2392-6140
https://scholar.google.no/citations?user=AWeghB0AAAAJ&hl=en
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