This question appears to arise from a comment I made in an earlier question.
Op had written:
The pie charts compare the amount of people enrolled on six courses,
in a certain college in the UK.
I had commented:
We would not normally say "amount of people" - either number of people (if you are showing actual numbers) or proportion of people (if using, say, percentages). amount is used for 'non-discrete' items (i.e. things that you cannot count, but can only measure e.g. by weight or volume, such as sugar or a liquid.
OP is now asking about the usage of amount is a sentence such as:
The number of people commuting by bus considerably increased in the year of 2013.
and asks whether amount or proportion could replace number.
Cambridge Dictionary defines amount as follows and includes a Grammar Note:
a collection or mass, especially of something that cannot be counted:
[example sentences omitted - see link]
Amount of or number of?
We use amount of with uncountable nouns. Number of is used with countable nouns:
- We use a huge amount of paper in the office every day.
- The amount of time it took to finish the job was very frustrating.
- A great number of students volunteer each year for environmental projects.
- Not: A great amount of students volunteer …
- I have a number of things I want to talk to you about.
The original sentence refers to "[comparing] the amount of people enrolled on six courses [using a pie chart]". The context clearly suggests that the actual numbers of student involved are known. In that instance, it seems that number or proportion (depending on the values actually shown in the pie chart) would be appropriate; and that amount would, at best, be non-idiomatic. That view is reinforces by the Grammar Note above indicating that "A great amount of students volunteer …" would be wrong.
In the second example sentence:
- amount may be more acceptable because there is (presumably) no reference to precise numbers;
- even so, number still sounds more idiomatic to me; and would refer to the overall (estimated) number of bus commuters using buses;
- proportion would be appropriate only if there were a comparison with (for example) the overall number of commuters.
But beware: in this case the difference between number and proportion could be important, because one value could go up while the other value goes down. For example:
- Year 1: 4 million commuters use the bus; 6 million use the train; hence 40% (of the total 10 million) use the bus.
- Year 5: 5 million commuters use the bus; 8 million use the train; hence 38.5% (of the total 13 million) use the bus.
Thus the number of bus commuters has increased by 1 million (23%), but the proportion of bus commuters has decreased by 1.5%.