BibTex format
@article{Haddaway:2017:10.1016/j.envint.2016.12.003,
author = {Haddaway, NR and Collins, AM and Coughlin, D and Kohl, C},
doi = {10.1016/j.envint.2016.12.003},
journal = {ENVIRONMENT INTERNATIONAL},
pages = {351--355},
title = {Including non-public data and studies in systematic reviews and systematic maps},
url = {http://dx.doi.org/10.1016/j.envint.2016.12.003},
volume = {99},
year = {2017}
}