Careless or sloppy — lacking attention, with many mistakes or faults (often read ずさん).
この報告書は杜撰で、数字の間違いが多い。
This report is sloppy and has many numerical errors.
杜撰な計画ではプロジェクトは成功しない。
A careless plan won't lead to a successful project.
締め切り前の杜撰な作業が原因でトラブルが起きた。
Trouble arose because of sloppy work done before the deadline.
As a noun-like use: work or a piece of writing that relies on unreliable sources or contains many errors; often seen as '杜撰な〜'.
あの記事は杜撰で、出典もはっきりしていない。
That article is unreliable and its sources are unclear.
杜撰な資料に基づいた論文は評価されない。
A paper based on unreliable materials will not be well regarded.