If there is one simple writing skill all graduate students should be taught, it is how to write comparisons correctly. There are several ways to mess up comparisons, but there is one I see very frequently, from native speakers and non-native speakers alike: compared to is used instead of the word than.
Here are some examples paraphrased from works I have edited:
“The sodium concentrations were higher in sample A compared to sample B.”
“Spring had a much higher percentage of readings above 100 μg/m3 compared to the fall.”
In both examples, compared to should simply be replaced with than:
“The sodium concentrations were higher in sample A than sample B.”
“Spring had a much higher percentage of readings above 1000 μg/m3 than fall.”
In some cases, a little more work is necessary to correct these second-degree comparisons. Here is an example:
“SOD1 mRNA was significantly elevated in tumors as compared to normal tissue.”
We need to change the word elevated to a comparative adjective and then switch the compared to to than:
“SOD1 mRNA was significantly higher in tumors than in normal tissue.”
Unfortunately, these errors are so common in scientific writing and everyday speech that they can be hard to catch. But pay attention to those comparative statements, see what happens if you replace compared to with than, and your scientific writing will be more clear and concise.