Use of plural with "respectively" when referring to a property

Question

If you are referring to one property but are giving the respective values for two different things do you use the singular or plural form? Can the property be treated as a mass noun so that it takes on a cumulative reference?

1. The yields of 1 and 2 were 76 and 89%, respectively.

   The yield of 1 and 2 was 76 and 89%, respectively.

2. In control and treated cells, the mean values were 8.6 and 7.5, respectively.

   In control and treated cells, the mean value was 8.6 and 7.5, respectively.

It's clear that the plural is used for cases in which two properties are listed (i.e., the yield and recovery rate of A were...) but it's not clear when only one propery is listed.

Answer 1

I agree that the plural form is correct. Or you could avoid the problem altogether by recasting the sentences as "The yield of 1 was 76% and that of 2 was 89%." and "The mean value of control cells was 8.6, and of treated cells, 7.5."

Answer 2

In sentence 1 of 1, the plural verb "were" refers to two subjects, yield of 1 and yield of 2. Even though the property, yield, is one, there are two values of a property for different objects that are being described later in the sentence.

In regard to the sentence 2 of 1, the usage of singular verb "was" do not correctly associate with multiple values. The usage of respectively do not map to multiple objects.

The issue is with the number of the subjects being referred to in the sentence.

Answer 3

The plurality of a property (i.e. a noun) in the relationship to the adverb "relatively" is irrelevant as the adverb attaches to the verb in this case. There is no verb+adverb aggreement.

The question should be what is the verb choice for the words "yield(s)" and "value(s)". In this case the verb must agree with the noun to which it applies and the standard rules for subject/verb agreement apply.

The inclusion of the preposition phrases "of 1 and 2" in example 1 and points to a problem in that while you can have a yield of 1 and 2, it is a single yield and should be expressed as a single unit x% and not X and Y%. This is more of a logical error than a grammatical one as English has no agreement rules appling to the objects.

Example 2 is the same problem, but seems more awkward because there is no intervening prepositional phrase which seems to act as a buffer betweem the subject and object in example 1.