  An analytical model invoking variations in the charge-carrier density is used
to generate magnetoresistance curves that are almost indistinguishable from
those produced by sophisticated numerical models. This demonstrates that,
though disorder is pivotal in causing linear magnetoresistance, the form of the
magnetoresistance thus generated is insensitive to details of the disorder.
Taken in conjunction with the temperature ($T$) dependence of the zero-field
resistivity, realistic levels of disorder are shown to be sufficient to explain
the linear magnetoresistance and field-$T$ resistance scaling observed in
high-temperature pnictide and cuprate superconductors. Hence, though the
$T$-linear zero-field resistance is a definite signature of the "strange metal"
state of high-temperature superconductors, their linear magnetoresistance and
its scaling is unlikely to be so.
