and passive voice
Yes, the passive voice helps when we need to use the third person perspective, as most work (at least quantitative work) requires. However, instead of passive voice you can use this: "The researcher"
(i.e. "The researcher distributed surveys to 100 people.")
seems odd to me to also use past tense when describing e.g. which kind of value a specific test procedure or questionnaire yields, or which kind of actions are necessary to conduct the test
yes, in this kind of case, you can switch tenses right in the middle of a paragraph.
You can even switch tenses in the middle of a sentence:
"The researcher used a survey that enables respondents to rate their feelings about..."
You are right. It is okay to use the present tense in that situation.
This is correct, as far as I know:
"
The degree of nicotine dependence was assesed by means of the Fagerstroem Test for Nicotine Dependence. Six items concerning nicotine consumption and craving for nicotine yield a score between 0 and 10 points to indicate the severity of nicotine dependence"