[R-sig-ME] Random slopes without random intercepts
Ken Beath
kjbeath at kagi.com
Thu Jan 17 12:45:54 CET 2008
On 17/01/2008, at 10:25 PM, Nathaniel Smith wrote:
> On Thu, Jan 17, 2008 at 11:11:31AM +0000, Nick Isaac wrote:
>> Basically, I want to explore the full volume of parameter space for
>> my
>> dataset. There's only one fixed effect, but several levels of random
>> variation. I can fit all combinations of random intercept and
>> random slope
>> models as:
>>
>> 1) lmer( y ~ x + (1|A) ...)
>> 2) lmer(y ~ x + (x|A) ...)
>>
>> The logical way to remove the random intercept is to remove "A"
>> from formula
>> 2. But then lmer wouldn't know which level at which to fit the random
>> slopes. I tried "A-1" and "(A-1)" but both returned errors.
>
> You want (x-1|A), or (x+0|A) -- the two are identical to each other.
>
It is very unusual to find data requiring a random slope but no random
intercept, as it requires that all lines pass through the same point
on the y axis.
Ken
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