[Tex/LaTex] AGSM bibliography style sometimes doesn’t abbreviate to “et al.” for duplicate author+year

bibtexcitingharvard-style

With BibTeX and the harvard/AGSM style, some references (from authors who have multiple papers per year) aren't abbreviated to "et al.", with the addition of a, b, et cetera. For example, with the code attached below, I get:

enter image description here

Only one paper is abbreviated to et al., the others not. Any idea why this is happening? The in-text references should be Basu et al. (2008a) and Basu et al. (2008b), which I believe AGSM should automatically do?

\documentclass[10pt,a4paper]{article}
\usepackage{natbib}

\begin{document}

\cite{basu2008a, basu2008b, beare2006}

\bibliographystyle{agsm} 
\bibliography{references.bib}

\end{document}

With BibTeX file (references.bib):

@string{jam="J. Appl. Meteor."}
@string{ag="Acta Geop."}
@string{blm="Bound.-Layer Meteor."}

@article{basu2008a,
  author={Basu, S. and Vinuesa, J.-F. and Swift, A.},
  title={Dynamic {LES} modeling of a diurnal cycle},
  journal=jam,
  year={2008},
  volume={47},
  number={4},
  pages={1156-1174}
}

@article{basu2008b,
  author={Basu, S. and Holtslag, A. A. M. and Wiel, B. J. H. and Moene, A. F. and Steeneveld, G. J.},
  title={An inconvenient "truth" about using sensible heat flux as a surface boundary condition in models under stably stratified regimes},
  year={2008},
  journal=ag,
  volume={56},
  number={1},
  pages={88-99}
}

@ARTICLE{beare2006,
 author={Beare,R. J. and Macvean,M. K. and Holtslag,A. A. M. and Cuxart,J. and Esau,I. and Golaz,J. -. and Jimenez,M. A. and Khairoutdinov,M. and Kosovic,B. and Lewellen,D. and Lund,T. S. and Lundquist,J. K. and McCabe,A. and Moene,A. F. and Noh,Y. and Raasch,S. and Sullivan,P.},
 title={An intercomparison of large-eddy simulations of the stable boundary layer},
 journal=blm,
 year={2006},
 volume={118},
 number={2},
 pages={247-272}
}

Best Answer

You've come across an unusual -- and admittedly rather severely under-documented -- feature (not a bug...) of the agsm bibliography style. Suppose two bib items labelled, say, AA and BB each have one or more authors. Crucially, suppose the total number of authors differs -- e.g., let bibitem AA have 3 authors and bibitem BB have 5 authors -- and suppose further that AA and BB share the same first author (say, XYZ) and the same publication year (say, 2000).

When this occurs -- as is the case in the example you've posted -- the agsm bibliography style does not set the citation call-outs as XYZ et al (2000a) and XYZ et al. (2000b), respectively. Instead, it lists all author names for both publications.

I suppose this is a fail-safe way of avoiding any kind of confusion over whose publication might be cited as XYZ et al. (2000a).

The only time when you do get the FirstAuthor et al (year) citation call-out pattern is if (a) the two publications have the same authors (and thus the same number of authors) as well as the same publication year and (b) there is no other three-or-more-author publication in the bibliography that features the same first author and publication year.

Again, this feature of the agsm style is both uncommon (to put it neutrally) and, unfortunately, quite obscure and under-documented. I wouldn't call it a bug, though. If you truly can't stand this feature, it's probably a good idea to start looking for an alternative bibliography style.

An MWE and screenshot:

enter image description here

\RequirePackage{filecontents}
\begin{filecontents}{testagsm.bib}
@article{1,
  author = "XYZ", title = "x", journal= "y", year = 2000}
@article{2,
  author = "XYZ and B", title = "x", journal= "y", year = 2000}
@article{3a,
  author = "XYZ and B and C", title = "x1", journal = "y", year = 2000}
@article{3b,
  author = "XYZ and B and C", title = "x2", journal = "y", year = 2000}
@article{4,
  author = "XYZ and BB and CC and DD", title = "x", journal= "y", year = 2000}
@article{5,
  author = "XYZ and BBB and CCC and DDD and EEE", title = "x", journal= "y", year = 2000}
@article{x1,
  author = "A and B and C", title = "D1", journal = "E1", 
  year = 3001, volume = 1, number = 2, pages = "3-4"}
@article{x2,
  author = "A and B and C", title = "D2", journal = "E2", 
  year = 3001, volume = 5, number = 6, pages = "7-8"}
\end{filecontents}

\documentclass{article}
\usepackage{natbib,har2nat}
\bibliographystyle{agsm}
\setlength\parindent{0pt} % just for this example

\begin{document}
\begingroup
\obeylines
\citet{1}
\citet{2}
\citet{3a}, \citet{3b}
\citet{4}
\citet{5}

\medskip
\citet{x1}, \citet{x2}
\endgroup

\bibliography{testagsm}
\end{document}
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