The phrase "about four topics" is correct and usable in written English.
It can be used when referring to a general estimate of the number of subjects or themes being discussed or covered.
Example: "In today's lecture, we will cover about four topics related to climate change and its impact on the environment."
Alternatives: "approximately four subjects" or "roughly four themes".
A 3-h lecture, which was about four topics approach to clinical ethical case analysis, was given to the students.
We asked the epidemiologists about four topics: Research context: aim, persons who give the assignment, financiers, collaborative partners, research method; Main outcomes of the research, considered important by epidemiologists; Follow up given to the results; Explanation of this follows up.
This chapter talks about two topics: simulation and digital control.
In this section, we are discussing about two topics related to the experiment results.
It aggregates data from about 100 sources including dictionaries, encyclopedias and covers about one million topics, which sounds like a lot until you consider how many possible topic areas there are.
The vaccinators were interviewed about two topics: their tasks during the program and whether they felt prepared, and how they thought the program could have been improved.
In many countries the print media, at least as captured in a global database, are largely silent about three topics central to evidence-informed health systems.
The focus of our media representation study was whether and how policymakers, stakeholders, and researchers talk in the media about three topics: policy priorities in the health sector, health research evidence, and policy dialogues regarding health issues.
Our focus was whether and how policymakers, stakeholders, and researchers talk in the media about three topics: policy priorities in the health sector, health research evidence, and policy dialogues regarding health issues.
He'd start talking to you about one topic, and then he'd end up in another topic and he wouldn't know how he got there".
One might wish for less breadth and more focus, however; often we barely have time to think about one topic when we are off to the next.
