Use respectively to show the correspondence between two series that each contain at least three items.

Example 1

Consider a field experiment conducted in the fall of the year. You could say:

1a: The mean temperature was 25 C in September, 20 C in October, 16 C in November, and 12 C in December. But note that there are two series (the temperatures and the months), each with four items. You can better indicate the change in temperature by first presenting one series and then the other, with respectively indicating their relationship:

2a:The mean yield was 10 kg per plot in the low-light treatment, 15 kg per plot in the medium-light treatment, and 12 kg per plot in the high-light treatment.

2b: The mean yield (kg per plot) was 10, 15, and 12 in the low-, medium-, and high-light treatment, respectively.

In the second example, use of respectively reduces the word count from 23 to 19.

Example 3

Do not use respectively if there is only one series in the sentence. Do not say:

3a: The mean temperature was 25, 20, 16, and 12 C, respectively.

In 3a, respectively provides no information. Delete it.

Example 4

Do not use respectively if there are only two items in each of the series. Do not say:

4a: The temperature was 25 and 20 C in September and October, respectively.

Although example 4a is not technically wrong, it needlessly complicates a simple statement. Consider that the writer's goal is to help the reader understand with minimum effort. Which is easier to understand and therefore more effective by definition?

4a: The temperature was 25 and 20 C in September and October, respectively.

4b: The temperature was 25 in September and 20 C in October.

Who would use respectively in this simple case? The answer is an inexperienced writer who wants to sound scientific and professional. Excessive or incorrect use of respectively is an example of inflated, bureaucratic prose. Use respectively only if it increases clarity and concision (see example 2b).