Although the telephone approach has been successful, several modules were not possible to ask by phone as they were not ideally suited to this mode of collection.
Er bod y dull galwadau ffôn wedi bod yn llwyddiannus, nid oedd yn bosibl gofyn am sawl modiwl dros y ffôn gan nad oeddent yn ddelfrydol ar gyfer y dull casglu hwn.