Hi,
How much is Mr. Krashen's word and how much is possible extra stuff added by the writer if you can tell from this one setence referenced? When you reference like this, how much should be Mr. Krashen's word? If the overall idea is his, but not word for word, can we reference like this? In an article named "Adapting Communicative Language Instruction in Korean Universities" by Gene Vasilopoulos at Daejeon University on The Internet TESL Journal, I found this: 

 This approach is similar to the way children learn their native tongue, a process that produces functional skill in the spoken language without theoretical knowledge (Krashen 1982).

Anonymous

“If the overall idea is his, but not word for word, can we reference like this?”

That's exactly how it must be written in the Harvard reference system.

Hi,

I think the example shows how the reference is made to Cormack's work (published in 1994?), ... ”

Yes, you got it right. It's the year in which the book was published

... but my question is, When you make such a reference, what is the barometer for measuring how exact (?) the your referencing wording has to be?" It doesn't look to be that it has to be written verbatim since you are not quoting. I think like indirect quoting, since you are not using the author's words quote for quote...”

Again, that's correct.
If you were copying the words used by the author(s), than you'd need to put them within quotation marks (if it's a short phrase or sentence) or to indent them in your text (if the quotation is long).
In the example about Cormack's work, the author is expressing with his/her own words (= paraphrasing) something that has been written by Cormack. S/he could be putting into a short sentence the main point of a huge book, or rephrasing a sentence that appears in Cormack's text. The important thing, when using this type of reference, is not to use the original words.
If you ask me what's the point, all I can answer is that guidelines (at least, the ones I've read!) suggest not putting too many direct quotations (that is, those enclosed in speech marks) in an essay/article/etc for a number of reasons:  i) they would make the essay less readable; ii) the essay would appear as a collection (patchwork?) of other texts, rather than a critical reflection on those; iii) the more direct quotations are in the essay, the less effective they would be - in other words, only put the most important direct quotations, the ones you want to emphasise.

... and using your words to note what the author said, there might be a slight chance of misinterpretation of the author's intent.”

If you're using referencing systems like this one, you're either writing an academic work (article/report/essay/dissertation/etc.) or a professional report, so you are writing either for somebody who will assess your piece of writing or for peers who know something about the topic. You don't want to misinterpret the text, do you?

Also, how the Harvard Style of Referencing differ from APA Style on the same topic area?”

Sorry, I can't answer. I've never used or studied the APA style.

Whatever you're writing, I wish you good luck!

Anonymous

“Thank you for your extensive response. You helped me a lot.

”

I'm really glad I could help. Please forgive me for any grammar mistakes I might have made in my posts.