[R-sig-ME] z-scores and glht
bbolker at gmail.com
Wed Apr 25 20:34:34 CEST 2018
If someone wanted to work hard enough they could probably work out a
Satterthwaite approximation for the degrees of freedom of these
contrasts ... ?
On 2018-04-25 02:25 PM, Dan Mirman wrote:
> The z-scores are computed by dividing the Estimate by the SE. As for why
> these are not t-statistics, the short answer is that the degrees of freedom
> are not trivial to compute. I believe Doug Bates' response is often cited
> by way of explanation:
> http://stat.ethz.ch/pipermail/r-help/2006-May/094765.html and it is covered
> in the FAQ:
> (for more discussion of alternatives see Luke, 2017,
> glht() is side-stepping all of that and just using a normal approximation.
> For what it's worth, my own experience is that this approximation is only
> slightly anti-conservative, so I usually feel comfortable using it.
> Hope that helps,
> On Wed, Apr 25, 2018 at 12:26 PM, Cristiano Alessandro <
> cri.alessandro at gmail.com> wrote:
>> Hi all,
>> something is wrong with my email, so I am sorry for possible multiple
>> After fitting a model with lme, I run post-hoc tests with glht. The results
>> are repored in the following:
>>> lev.ph <- glht(lev.lm, linfct = ph_conditional);
>>> summary(lev.ph, test=adjusted("bonferroni"))
>> Simultaneous Tests for General Linear Hypotheses
>> Fit: lme.formula(fixed = data ~ des_days, data = data_red_trf, random =
>> ~des_days |
>> ratID, method = "ML", na.action = na.omit, control = lCtr)
>> Linear Hypotheses:
>> Estimate Std. Error z value
>> des_days1 == 0 3232.2 443.2 7.294 9.05e-13 ***
>> des_days14 == 0 3356.1 912.2 3.679 0.000702 ***
>> des_days48 == 0 2688.4 1078.5 2.493 0.038025 *
>> I am trying to understand the output values. How are the z-scores computed?
>> If the function uses standard errors, should these be t-statistics (and not
>> Thanks for your help, and sorry for the naive question.
>> [[alternative HTML version deleted]]
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