  We characterize effective descent morphisms of what we call filtered
preorders, and apply these results to slightly improve a known result, due to
the first author and F. Lucatelli Nunes, on the effective descent morphisms in
lax comma categories of preorders. A filtered preorder, over a fixed preorder
$X$, is defined as a preorder $A$ equipped with a profunctor $X\to A$ and,
equivalently, as a set $A$ equipped with a family $(A_x)_{x\in X}$ of upclosed
subsets of $A$ with $x'\leqslant x\Rightarrow A_x\subseteq A_{x'}$.
