The studies that analyzed words per main clause also evaluated subordinate clauses per main clause:

In essence, subordinate clauses involve embedding one whole main clause into another. As a result, subordinate clauses are a major indicator of syntactic maturity.

Levels of Embedding

     The traditional approach to grammar is to teach students what constructions, such as clauses, are, and then to stop. This overlooks the fact that much of syntactic maturity involves embedding one construction into another. In the following sentence, for example, the "that their skirts" clause is embedded in the "if" clause:

[If the women would have dressed {like others} or seen [that their skirts bothered the work {of others} {in their occupation}]] they would have seen [that their supervisor was just doing his job.]

In this example, the "if" clause is considered as embedded at level one; the "that" clause, at level two. The followiing example (from s95pr05) includes two clauses embedded at level three:

\-\One thing [that seems to be the problem] is [that the women think [that they can dress, or undress [as the case may be,] as much [as they feel necessary to lure or distract the man {from his job.}]]]

Level three is relatively rare among student writers, and even professional writers rarely embed clauses at level four.
     The studies presented at this web site attempt to at least begin the study of embedding as an aspect of syntactic maturity. Clauses embedded in other clauses have been counted and calculated. This is, however, only a beginning because it does not take into consideration such things as clauses embedded onto an appositive. Consider the following:

Although in the Spring 95 study, the "which" clause would count as a level one, it can be viewed as an even more sophisticated construction because it modifies the appositive "city," and appositives can be considered as reduced clauses. (See Semi-Reduced Clauses, below.)

     For the experienced, subordinate clauses are generally easy to recognize. In the analyzed texts, they are placed in brackets. [ ] But as with prepositional phrases, questions arise, especially if one is counting words and constructions.

Subordinate Clause or Prepositional Phrase?

     I expect this section to become rather long as I collect and add examples, and I expect a lot of English teachers (and especially linguists) to disagree with me. What they will probably want to consider a subordinate clause, I will accept (and count) as a prepositional phrase. Consider the following sentence (s95pr01):

Years ago, I would have considered "as women" as the remnant of an ellipsed subordinate clause: "as women call for sexual harrassment." As I used the KISS approach with students, I noted that many students were marking such things as prepositional phrases.
     From their point of view, that makes sense. The directions tell them to find the "preposition," and to ask the question "what?" after it. If whatever answers that question is a sentence, they do not have a prepositional phrase. I could, of course, have added "is or is part of a sentence," but I decided not to. From my experience, students have enough on their hands just remembering that "if it is a sentence, it is not a prepositional phrase." Indeed, many of the analytical errors that they make (another interesting topic for research) involve including part of a subordinate clause in a prepositional phrase. For example, they might mark the following: "He went {to bed} {after his father} came home." It takes a while for some students to see that, if they were asked the question, "After what?", according to the sentence, the answer is "after his father came home." It seemed to me that, at this stage, the question of ellipsed clauses as objects of prepositions is beyond their zone of proximal development. I simply decided to accept such constructions as prepositional phrases, and, if necessary, return to them after students had been working on clauses for a while.
     I am aware of some cases where this will cause a problem, but I have also noted instances in which what appears to be a subordinate conjunction might better be viewed as a preposition. As I go through the analyzed examples of students' writing, I will discuss some of them here.

(from P1_01):
\-\{In the united states} there are more Blacks put {in jail} {than Whites.}

(from P1 02):
\-\Either way is {at least} twenty miles farther {than taking the straight path there, Route 262.}

     I can imagine someone saying or writing "In the United States, there are more Blacks put in jail than there are Whites put in jail." In other words, I can see an argument for considering "than" in the first example as a subordinate conjunction introducing a partially ellipsed clause. However, would anyone ever say "Either way is at least twenty miles farther than taking the straight path there, Route 262, is far"? Not only would no one ever say this, but it denies the sense of the original, which is that the straight parth is, relatively speaking, short. Linguists may continue to argue about this, but for students, isn't it easier to consider "than," in many cases, as a preposition?

Semi-Reduced Clauses

     There is reason to consider appositives and gerundives as reduced subordinate clauses. For example, Bob loves spaghetti, which is an Italian food. can be reduced to Bob loves spaghetti, an Italian food. In some cases, either because of the nature of the clause or the writer's processing capability, the clause is not completely reduced, and is therefore considered "semi-reduced." Most cases involve adverbial clauses:

When we were going to the store, we saw Santa.[not reduced]
When going to the store, we saw Santa. [semi-reduced]
Going to the store, we saw Santa. [reduced to a gerundive]

In the Spring 95 study, for reasons of time, semi-reduced clauses were simply counted as clauses. Reduction, the result of deletion (ellipsis), is, however, a major factor in syntactic maturity. I hope to return to this question, and invite others to pursue it. Consider the following

(from s95pr06):

\-\[When dealing {with the public} {in a job} {such as described}] there should be a certain amount {of professionalism} outwardly shown.

The initial "When dealing" obviously means "When *someone is* dealing." But the sentence presents an even more interesting problem in the phrase I have marked as prepositional -- "such as described." Here again we are dealing with ellipsis. (It would be interesting to see how traditional grammarians deal with this.) In effect, the "prepositional phrase" means "such as that which was described." If you examine the student's writing (s95pr06), you will see that he is a heavy user of subordinate clauses, and one has to wonder to what extent such reductions are further evidence of syntactic maturity.

(from s95pr59):
\-\There are just to many factors [that have to be considered [when trying to tackle such an issue {as this one.}]]

"IF"

     Because "if" functions exclusively as a subordinate conjunction, it was always counted as introducing one, even when the clause itself was largely ellipsed:

(from s95pr16):
\-\Is there a dress code? \-\[If so,] were the women violating it?

Compounded Subordinate Clauses

     I am not sure of the degree of the problem, but there certainly is a problem in deciding whether some clauses are subordinate or main. In most cases, these are clauses which could be compound direct objects. Consider the following examples:

(from s95pr09):

\-\Finaly, I feel [that the two women were not {at fault,}] \-\and [the employer should develop a dress code [if he has a problem {with the length} {of skirts.}]]

(from s95pr14):

\-\Is the supervisor over reacting \-\or is he just jelous [because the women are hot] and [he has an ugly wife,] and [the women wont give him the time {of day.}]