survey weights

Hi all, I've been trying to get a large (12mb) Stata
survey database into R. I managed that, but when I
attach survey weights, something goes wrong. The error
message is: object dchina not found. Here's the
script:

library(car)
library(foreign)
library(survey)

China <- read.dta("C:/final07c2.dta")
attach(China)

data(China)

dchina<-svydesign(id=~psu,strata=~strata,weights=~weight0x,

summary(dchina)

On Sat, 3 Sep 2005, A Das wrote:

Hi all, I've been trying to get a large (12mb)

Stata

survey database into R. I managed that, but when I
attach survey weights, something goes wrong. The

error

message is: object dchina not found. Here's the
script:

If that is the *first* message then something
extremly strange is 
happening

library(car)
library(foreign)
library(survey)

China <- read.dta("C:/final07c2.dta")
attach(China)

This attach() isn't necessary or helpful

data(China)

You should get a warning here

Warning message:
data set 'China' not found in: data(China)

since China isn't one of the built-in data sets. If
you don't get this 
message it suggests that you do have a built-in
dataset called China, 
which will have overwritten your file.

                          data=China,nest=TRUE)

If this line doesn't produce an error message then a
variable called 
"dchina" must have been produced, in which case you
shouldn't get an error 
message saying it wasn't found in the next line.

summary(dchina)

Are you sure there wasn't an earlier error message
from the call to 
svydesign()?

 	-thomas

Thanks, Thomas.
   Yes, that's exactly what happened: the warnings
came first after "data(China)", and then after
"dchina<-svydesign..." So the design object isn't
being produced? The dataset is very large, and the
weights were already set in Stata before importing.
Would either of those cause problems?

On Sun, 4 Sep 2005, A Das wrote:

Thanks, Thomas.
   Yes, that's exactly what happened: the warnings
came first after "data(China)", and then after
"dchina<-svydesign..." So the design object isn't
being produced? The dataset is very large, and the
weights were already set in Stata before

importing.

Would either of those cause problems?

Probably not.  What was the error message from
svydesign()?  That is what 
will say what went wrong.

 	-thomas

Just: "missing values in object". That would imply the
object was created. But then I write "dchina", and it
says "object dchina not found".

                         -Bobby

--- Thomas Lumley <tlumley at u.washington.edu> wrote:

On Sun, 4 Sep 2005, A Das wrote:

Thanks, Thomas.
   Yes, that's exactly what happened: the warnings
came first after "data(China)", and then after
"dchina<-svydesign..." So the design object isn't
being produced? The dataset is very large, and the
weights were already set in Stata before

importing.

Would either of those cause problems?

Probably not.  What was the error message from
svydesign()?  That is what
will say what went wrong.

 	-thomas

On Sun, 4 Sep 2005, A Das wrote:

Just: "missing values in object". That would imply

the

object was created. But then I write "dchina", and

it

says "object dchina not found".

No, it would not imply the object was created.  If
it was an error message 
(rather than a warning) the object would not have
been created.

I presume the full message was
  Error in na.fail.default(object) : missing values
in object

If so, it sounds as though you have missing values
in the id, weights, or 
strata variable.
    summary(China[,c("psu","stata","weight0x"])
will verify this.

Stata will just have dropped these observations (use
-svydes- to verify 
this).  If you want to drop the observations in R
you need to do this 
explicitly. Having missing data may be unavoidable,
but if you have 
observations in a sample it seems that you should
know how they were 
sampled.
To drop these observations you could use

obsChina <- subset(China, !is.na(psu) &
!is.na(strata) & !is.na(weight0x))

and then use obsChina rather than China in the
svydesign() function.

 	-thomas

                         -Bobby

--- Thomas Lumley <tlumley at u.washington.edu>

wrote:

On Sun, 4 Sep 2005, A Das wrote:

Thanks, Thomas.
   Yes, that's exactly what happened: the

warnings

came first after "data(China)", and then after
"dchina<-svydesign..." So the design object

isn't

being produced? The dataset is very large, and

the

weights were already set in Stata before

importing.

Would either of those cause problems?

Probably not.  What was the error message from
svydesign()?  That is what
will say what went wrong.

 	-thomas