The population of Japan is lower than Thailand.
Here is an example of not ‘comparing like with like’.
In the noun phrase ‘the population of Japan’, ‘population’ is the main noun. ‘Population’, which is a mass of people, is said to be lower than ‘Thailand’, a land mass. This leaves the reader with an image of Thailand hovering up in the air, with the Japanese population some physical distance below it!
A mass of people is not like a land mass. In order to make sure that you’re ‘comparing like with like’, use a parallel structure:
This may result in some repetition – ‘the population of’ is used twice. But don’t worry about repetition. At least you’re ‘comparing like with like’.
Repetition can be avoided in this kind of comparative structure by substituting ‘that’ for part of the phrase that you’re trying not to repeat:
In this example, that replaces the population, but it can be used to replace any noun or noun phrase.