[R] Metafor -can't calculate heterogeneity with non-positive sampling variances

[Owen, Branwen]

Hi, I'm doing a meta-analysis in metafor. All is fine except when there are 0s in the values that i'm pooling, then i get a pooled estimate but not the I2 that i am also interested in.
for example:

summary(rma.1<-rma(yi,vi,data=mix,method="ML",knha=F,weighted=F,intercept=T))
(where yi are the study outcomes, one of which is 0, and vi is the variance of the study outcomes)

Random-Effects Model (k = 17; tau^2 estimator: ML)

  logLik  deviance       AIC       BIC      AICc  
 13.0539       Inf  -22.1077  -20.4413  -21.2506  

tau^2 (estimated amount of total heterogeneity): 0.0119 (SE = 0.0043)
tau (square root of estimated tau^2 value):      0.1089

Model Results:

estimate       se     zval     pval    ci.lb    ci.ub          
  0.1837   0.0274   6.7154   <.0001   0.1301   0.2374      ***

---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

Warning messages:
1: In rma(yi, vi, data = mix, method = "ML", knha = F, weighted = F,  :
  There are outcomes with non-positive sampling variances.
2: In rma(yi, vi, data = mix, method = "ML", knha = F, weighted = F,  :
  Cannot compute Q-test, I^2, or H^2 with non-positive sampling variances.

Is there any way around this?
thanks
Branwen
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From: r-help-bounces at r-project.org [r-help-bounces at r-project.org] on behalf of r-help-owner at r-project.org [r-help-owner at r-project.org]
Sent: 27 August 2014 13:36
To: Owen, Branwen
Subject: Metafor -can't calculate heterogeneity with non-positive sampling variances

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