Explaining the need to avoid horizontal scroll

Question

I need help explaining to my boss why her design is poor on a client\'s website. She has no knowledge of the web, and it can be difficult as a web developer working with a

Answer 1

Point her to Nielsen - on of the most famous and top level web usability experts.

"Horizontal Scrolling" is error #3 in "Top Ten Web-Design Mistakes of 2002" article

Also, point out (not sure if Nielsen does) that vast majority of mice don't have horizontal scroll wheels (that was a point made in comments of an article discussing Nielsen's article).

Also, do the usual UI thing - TEST!

Pick 5 random people who ideally match the desired user profile. Ask them to use the mock-up with and without warning and observe which one's easier/faster (and ask, but also obseve without asking)