user interface - Autocomplete vs Drop-down. When to use? -

i've read somewhere (can't remember/find where) article web usability describing when use drop downs , when use autocomplete fields.

basically, article says human brain cannot store more last 5 options presented choose.

for example, in profile form, there current occupation, , system gives bunch of options, when read sixth options, brain can't remember first 1 anymore. example great place use autocomplete field, user types thinks occupation , select better few options filtered.

i hear opinion subject.

when should use drop-down , when should use autocomplete field?

for limited list, don't use autocomplete edit box or combobox, use listbox values visible @ once. limited lists, static content of 8 items, takes real estate, presents user better immediate overview.

for less 5 items radiogroup or checkbox group (multiple selections) may better.

for lists content dynamic, list of contacts, (scrolling) listbox or combobox appropriate because never know how many items in list. keep manageable, need allow kind of filtering and/or autocomplete.

autocomplete suffers fact users types needs match string beginning. hate except when used complete value based on typed in (type of) field before. e.g. browsers nowadays offer when filling out online forms.

allowing user start typing in combobox suffers same drawback. admittedly doesn't need if filtering based on "like %abc%" instead of "starts abc"

when dealing lists can have many similar items, way gmail's "to" field handles it. start typing any part of someone's name or e-mail address , gmail drop down list presenting contacts name or e-mail address contains characters have typed far anywhere within them. using , down keys changes selection in dropped down list (without affecting have typed) , pressing enter adds selected item "to" field. far best user experience have had far when having select list.

haven't found components yet can this, it's not hard "fake" combining edit box , listbox drops down when start typing , has contents filtered based on has been typed far.