Research instruments refer to the tools used in data collection for your study. They will include questionnaires, interview schedules and focus group discussions.
Questionnaires are mainly used to collect quantitative data, while interview schedules and focus group discussions will be used to collect qualitative data.
The decision whether to use questionnaires, interview schedules or Focus Group Discussions will be determined by the nature of your research, sample population number, and consultation with experts including your supervisor. Questionnaires are mainly used when the sample population is large (20+ people), since it is easier to handout questionnaire leaflets. Interview schedule and focus group discussions are used for smaller sample groups (usually less than 20 people).