Sentences involving comparisons often contain implied verbs. The missing verbs sometimes make it difficult to tell which pronoun case is correct. For example, which of the following sentences is correct?

He can't type as quickly as I.
He can't type as quickly as me.

To determine which is correct, fill in the implied verbs:

He can't type as quickly as I can.
He can't type as quickly as me can.

The first sentence is clearly correct. More examples follow.

She is taller than him.
She is taller than he (is).
We have a smaller yard than them.
We have a smaller yard than they (do).
I want a hat like him.
I want a hat like his.

Sometimes leaving the verb implied makes a sentence ambiguous, as in the following example:

She likes him better than me.

This sentence can be interpreted in two ways:

She likes him better than I do.
She likes him more than she likes me.