I'm reviewing a site and want to look at whether or not the existing drop-down menu is appropriate. Do people have evidence from user testing sessions (that they can share) on the effectiveness of drop-down menus, and in what situations/context these are appropriate. A Google search hasn't yielded any good results I can see so I'm hoping this community can help.
In larger sites, it's preferred to have mega-dropdown menus rather than standard dropdown-menus (where you might need to scroll to see all the options). In this case a Mega dropdown menu works very well since users don’t have to rely on short term memory (when scrolling) and it’s faster to navigate. Only one required step instead of three with usual navigation.
Look at an online clothes shop. Regular navigation uses hierarchy like Clothes > Men’s ware > T-shirts and Vest instead of the image below:
When designing you should group the options in larger meaningful chunks of information making the dropdown even more easy to use. Grouping is important not only to the layout of the web page but also on larger elements as well, such as a drop down menu.
Jakob Nielsen have tested it on real users and presents it in his article Mega Drop-Down Navigation Menus Work Well. In the article you’ll find other topics such as Simplicity, Accessibility and Speed (in terms of timing) which would cover your question.
To summarize; use dropdowns when you have a lot of content which need to be found fast, such as an online store. Competition is only a click away.