  Recently a number of studies have proposed that the dispersion along the star
formation rate - stellar mass relation ($\sigma_{\mathrm{sSFR}}$-M$_{*}$) is
indicative of variations in star-formation history (SFH) driven by feedback
processes. They found a 'U'-shaped dispersion and attribute the increased
scatter at low and high stellar masses to stellar and active galactic nuclei
feed-back respectively. However, measuring $\sigma_{\mathrm{sSFR}}$ and the
shape of the $\sigma_{\mathrm{sSFR}}$-M$_{*}$ relation is problematic and can
vary dramatically depending on the sample selected, chosen separation of
passive/star-forming systems, and method of deriving star-formation rates
($i.e.$ H$\alpha$ emission vs spectral energy distribution fitting). As such,
any astrophysical conclusions drawn from measurements of
$\sigma_{\mathrm{sSFR}}$ must consider these dependencies. Here we use the
Galaxy And Mass Assembly survey to explore how $\sigma_{\mathrm{sSFR}}$ varies
with SFR indicator for a variety of selections for disc-like `main sequence'
star-forming galaxies including colour, star-formation rate, visual morphology,
bulge-to-total mass ratio, S\'{e}rsic index and mixture modelling. We find that
irrespective of sample selection and/or SFR indicator, the dispersion along the
sSFR-M$_{*}$ relation does follow a 'U'-shaped distribution. This suggests that
the shape is physical and not an artefact of sample selection or method. We
then compare the $\sigma_{\mathrm{sSFR}}$-M$_{*}$ relation to state-of-the-art
hydrodynamical and semi-analytic models and find good agreement with our
observed results. Finally, we find that for group satellites this 'U'-shaped
distribution is not observed due to additional high scatter populations at
intermediate stellar masses.
