Both alternatives are possible, depending on the nature of your research question. What are your research questions? Is this prevalence and incidence? - There will be option 2 with a follow-up. If you want to study how the PFT method corresponds with the questionnaire, and/or outcomes of people with respiratory symptoms, it is option 1.

Thank you, ma'am, for your response. Our study has only 1 objective: prevalence and determinants of chronic respiratory illnesses in India. We need your guidance on which screening tool and diagnostic can fulfil our objective criteria

Start with validated questionnaire (eg; SGRQ). Is this questionnaire and scoring done by trained research person or by the participant? Smoking history and occupational history should be recorded.

Next step: check correlation of SGRQ score with PFT in a sample size (>100). (advise include those with both high and low scores)

Based on the above you can decide whether both are needed or questionnaire alone will suffice.