  Context: The mass-metallicity relationship (MMR) of star-forming galaxies is
well-established, however there is still some disagreement with respect to its
exact shape and its possible dependence on other observables. Aims: We measure
the MMR in the Galaxy And Mass Assembly (GAMA) survey. We compare our measured
MMR to that measured in the Sloan Digital Sky Survey (SDSS) and study the
dependence of the MMR on various selection criteria to identify potential
causes for disparities seen in the literature. Methods: We use strong emission
line ratio diagnostics to derive oxygen abundances. We then apply a range of
selection criteria for the minimum signal-to-noise in various emission lines,
as well as the apparent and absolute magnitude to study variations in the
inferred MMR. Results: The shape and position of the MMR can differ
significantly depending on the metallicity calibration and selection used.
After selecting a robust metallicity calibration amongst those tested, we find
that the mass-metallicity relation for redshifts 0.061< z<0.35 in GAMA is in
reasonable agreement with that found in the SDSS despite the difference in the
luminosity range probed. Conclusions: In view of the significant variations of
the MMR brought about by reasonable changes in the sample selection criteria
and method, we recommend that care be taken when comparing the MMR from
different surveys and studies directly. We also conclude that there could be a
modest level of evolution over 0.06<z<0.35 within the GAMA sample.
