Many writers beginning in the 1970s wanted to avoid gendered language.
In particular many academic writers, male as well as female, wanted to break the older habit of always using "he" to mean "he or she", and came up with different approaches.
You will find:
- Some writers alternate between "he" and "she" (some readers find this confusing)
- Some writers always use "s/he", "she/he" or "she or he" (some readers find this ugly)
- Some writers use "he" (some readers find this sexist)
- Some writers use "she" (some readers find this confusing, some find it mannered)
- Some writers use plural-as-singular-of-indeterminate-gender "they" (some readers find this confusing)
- Some writers use second-person ("... a rational DM ... If you were ...", some readers find this too informal)
- Some writers always have plural examples ("... rational DMs .... If they were ...", some readers find this dull)
- Some writers give the abstract people names mnemonic of their roles ("Alice and Bob" in cryptography, who then are naturally she and he. Some readers find this infantile)
- Some writers never use pronouns (".... a rational DM ... If that DM were ...", some readers find this repetitive)
- Some writers give the abstract people letters ("a rational DM X ... if X were ...", some readers find this legalistic or abstract)
All of these approaches have their merits and are widely seen. Each one also has vocal critics.
This and many related issues are covered very well in The Nonsexist Word Finder: A Dictionary of Gender-Free Usage, Rosalie Maggio, Beacon Press (1989). ISBN 0807060011.
Should you do the same?
First: it's worth noting that gender-mismatch errors are extremely confusing to native English speakers. The very common mistranslation of French "Un homme et sa mère" as "A man and her* mother" is confusing and the listener may well ask "whose mother?". Number-mismatch is much less confusing: "Apple is a big company. They are always seeking profit.", here "they" clearly refers to the "[The people of] Apple".
The following are my opinions, and you will certainly get other advice.
It depends entirely on your audience. I would suggest one of the easiest ways for a non-native writer, in technical or scientific writing, to avoid any unintended bias is to use "she/he" and "her/his" (equally the other way "he/she".) No one will give it a second glance or find it confusing, it's not dated, it's not in any way niche, and it's not sexist.
In spoken English (and websites), always-second-person is probably the most common. People under about 50 are also very likely to use singular-they. However, in this particular field (economics/operational research) precision about number looks important (an individual's actions with or against the herd, for example) so I'd suggest you might want to avoid it.