Non-exact matching will look for any occurrence of a keyword within your keyword phrase on the page being analyzed. Non-exact matching is the default and is activated when the exact matching checkbox is left unchecked on the first tab of the Page Critic screen.
Non-exact matching will return higher frequency counts on average than exact searches since ANY word in the keyword phrase is counted as a partial "hit." This is regardless of whether the words appear together on the page. The formula for computing frequency for non-exact searches is:
Number of times ANY of the words in your keyword or phrase appears on the page, DIVIDED by the number of words in the phrase
For example in the following paragraph:
"Computer programmers write the instructions that a computer reads."
If our keyword was computer programmers then the frequency above for an exact match would be one.
A frequency of 1.5 would be returned if we were doing a non-exact match. That's because we count "Computer" as one match, "programmers" as another match, and "computer" again as a third match. We then we divide by the number of words in the phrase, two in this case, which yields a frequency of 1.5. You can think of it as using the phrase "computer programmers" one and a half times on the page.
Most search engines appear to assign some relevance to keywords within a phrase even if they do not always appear together on the page. Therefore, you'll normally want to compare your page to your competitor's in non-exact mode since it will often give you a clearer picture of why a page ranks the way it does. In addition, most users will conduct searches on multiple words, but will not surround them in quotes to specify an exact search.