In the methods section one would use past tense due to what they have done was in the past. It has been debated whether one should use active or passive voice. The scientific journal Nature states ...

However, changing the tense deliberately can have a positive impact on your reader. For example, if you were writing a persuasive speech you may swap from the past tense to the present tense to ...

using ‘have’ in place of had in that particular conditional clause would be totally wrong just as the choice of the tense in the main cause it is introducing should be consistently past ...

However, changing the tense deliberately can have a positive impact on your reader. For example, if you were writing a persuasive speech you may swap from the past tense to the present tense to ...