Using respectively correctly

Respectively is a very useful word in scientific writing; however, we often see this word used incorrectly.

Here are some sentences that use the word “respectively” in the wrong way.

Can you identify what’s wrong with each sentence?

1. The P53, Bcl2 and Bcl-x antibodies were purchased from Cell Signaling and Invitrogen, respectively.
2. The leaves and flowers and were used for RT-PCR, Western blotting and immunofluorescent staining, respectively.
3. Proliferation was measured using the MTT assay and flow cytometry, respectively.
4. Expression of VEGF, MDM-2 and GAPDH, respectively, were quantified using real-time RT-PCR .
5. The 3 and 5-year overall survival and disease-free survival rates were 99.0%, 89.2%, 85.6% and 79.0%, respectively.
6. The mean and median values in control and treated cells were 8.6, 7.5, 8.9 and 7.2, respectively.

Did you spot what’s wrong with each example? Let’s look at them in turn….

Use respectively to link two groups that contain the same number of items

There are two groups of items in all of the examples above. I have highlighted the two groups of items in example 1 and 2 in bold below:

1. The P53, Bcl2 and Bcl-x antibodies were purchased from Cell Signaling and Invitrogen, respectively.

In example 1, three antibodies were purchased from two companies, so we can’t tell exactly which antibody came from each company.

2. The leaves and flowers and were used for RT-PCR, Western blotting and immunofluorescent staining, respectively.

In example 2, three techniques were listed for two different samples, so it’s not clear what sample was analysed by each technique, or if both leaves and flowers were analysed using all three techniques.

In these cases, it’s probably best not to use respectively, and you should write the information in full so your reader can understand exactly what you mean:

1. The P53 antibody was purchased from Cell Signaling and the Bcl2 and Bcl-x antibodies were purchased from Invitrogen.
2. The leaves were subjected to RT-PCR and the flowers were used for Western blotting and immunofluorescent staining.

Each group should have more than one word

Respectively should only be used to describe two or more items.

Respectively is not required in example 3, as proliferation was measured using both techniques, or in example 4, as expression of all three genes was quantified using real-time RT-PCR. Therefore, the correct sentences are:

3. Proliferation was measured using both the MTT assay and flow cytometry.
4. Expression of VEGF, MDM2 and GAPDH were quantified using real-time RT-PCR.

Make sure the connections and order of the words in each group are clear

Examples 5 and 6 are sentences that can cause a lot of confusion. There are the same number of words in each group, but the true order of the results is not very clear.

For example, in example 5, the 3-year overall disease-free survival rate could be either 89.2% or 85.6%. With these types of sentences, it is better to write the data out in full to be clear. Try something like:

5. The 3- and 5-year overall survival rates were 99.0% and 85.6% and the 3- and 5-year disease-free survival rates were 89.2% and 79.0%, respectively.
6. In control and treated cells, the mean (and median) values were 8.6 (8.9) and 7.5 (7.2), respectively.

Don’t use respectively in place of both, all, individually or separately

Often respectively is wrongly used to indicate that a experimental technique was used to analyse several samples. Examples 2, 3 and 4 fall into this category. In these cases, it is better to use the words “both” or “all”.

2. The leaves and flowers were used for RT-PCR, Western blotting and immunofluorescent staining.
3. Proliferation was measured using both the MTT assay and flow cytometry.
4. Expression of VEGF, MDM2 and GAPDH were quantified using real-time RT-PCR .

If you didn’t see the mistakes in the examples at the start, then I hope reading these rules and seeing the correct way to write sentences with respectively has helped.

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