The beginning of a literature review generally starts with a sentence summarizing previous research. Use of an incorrect verb tense is a very common mistake.
Which is the correct verb tense?
Can you explain the difference?
- Various studies examined the impact of Covid-19 on educational inequality.
- Various studies have examined the impact of Covid-19 on educational inequality.
When speaking generally about previous research, the present perfect is generally used. Thus number 2 is the correct answer. The reason is that the present perfect is used to link the past with the present. In sentence 2, have examined means the studies until the present.
The simple past is used for finished actions in the past so sentence 1 would mean specific studies done in the past. An English speaker would most likely be wondering which studies and when they were done. A citation would commonly be used.
Referring to previous research
These are general guidelines. The difference is not always completely black and white.
present perfect tense: used when writing about previous research in general; the research to the present
simple past tense: used when writing about specific research; often used with a citation