The Biometrical Journal is a leading journal in biometry. It is calling for papers for a special issue on "Models for continuous data with a spike at zero".

Zero-inflation models for count data have a long history and a huge amount of published research exists to the topic. In fact, the Biometrical Journal has contributed numerous papers to this area since zero-inflated count data are a prominent problem in the life-sciences. See, for example, the September 2013 issue of the Biometrical Journal.
In this call, we would like to draw the attention of the research community to another prominent problem in the life sciences: continuous data with a spike at zero. The extra-zeros can arise out of many reasons and it is not necessarily clear how they could be handled. A frequent problem is the occurrence of data below a limit of detection (LOD). In these cases, it might be reasonable to treat them as left-censored. A further modeling alternative could be that of employing so called two-step models, where at the first stage a binary variable describes whether or not the observed value is above the limit of detection while, at the second stage, a continuous variable is used to describe positive measurements. In other cases, it is less clear how to approach the problem. For example, consider the consumption of alcohol measured on a continuous scale. Then, there is a spike at zero representing the non-drinkers. The zeros are neither left-censored nor interval-censored.  Here, there are at least two problems involved. For one, the quantity of interest is bounded below, and for two, the zeros create a single mass distribution.  A further empirical application where extra-zeros may arise is when modeling length of stay in hospital admissions. This is frequently modeled following a count data approach, although the underlying quantity is continuous.  In length-of-stay situations, day surgery patients may be classified as having a null length of stay but, for administrative purposes, it could be necessary for them to be considered together with in-hospital patients whose length of stay is positive. Hence, we have a continuous quantity bounded below by zero and a spike at zero. 
In a regression context, we also think that these spikes could occur on the left-hand side of a regression equation as well as on the right-hand side, i.e. for the dependent (outcome) and the independent (predictor) variables

With  this call for submissions we are looking for novel contributions presenting 
•	authentic continuous data with  excess-zeros 
•	novel statistical approaches to handle these issues.
•	up-to-date case studies which address the above issues  and are of interest for the biometric community.
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Authors, who are not sure whether their problems and ideas fall under the call or not, may approach the Editors with an initial draft of the paper. 

All submitted papers under this call will undergo the standard review process of the journal. The deadline for papers for this call is May 31, 2014. 

The special issue is handled through the website of the Biometrical Journal and is handled as any other paper submitted to the journal except that the editing and the review process is handled by the Special Issue Editors  Dankmar Böhning and Marco Alfó.       
 
Please submit your manuscript at is http://mc.manuscriptcentral.com/biomj
 
 
To submit to the special issue login at MC (manuscript central), indicate at Step 1 that the submission is to a special issue and at Step 4 of the submission process enter "ZERO I" in the Special Issue Information field.
 
Submitted manuscripts should comply with the instructions for authors of Biometrical Journal which you find on the Biometrical Journal homepage using the link to the Author Guidelines.

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