I've never tried this, but it should work:

1. Make a list of 10 websites - half of them with splash screens;
2. Sit your client in front of a computer;
3. Explain that users hate slow websites and bounce rates are up;
4. Hand the list to your client and ask them to visit the "About us" page of all 10 websites.
5. Make sure the client visits all 10 pages. If they give up, remind them that users typically visit many more websites in a single web session.

Follow these steps and you'll be fine:

1. Make a list of 10 websites - half of them with splash screens;
2. Sit with your client in front of a computer;
3. Ask your client to visit the "About us" page of each site.
4. Make sure your client visits all 10 pages.

Then explain to your client that

• users visit much more than 10 pages in a single session.
• users are impatent
• bounce rates are up because of splash pages.