It is never too early to start thinking about how you will collect your quantitative data. I have frequently seen students wait until the methodology chapter to even begin considering how data will be gathered. By delaying on this decision, students place themselves at risk for significant push-backs by their committee, school reviewers, and the IRB. After identifying the topic of interest, it is best to consider at this juncture: should I administer a survey instrument or should I search for archival data within a third party?
If administering a survey, you must thoroughly search the literature for previously validated instruments to measure the variables of interest. Once you have identified a group of potential instruments, select the most well-established instrument (i.e., check how many times it has been cited) or the instrument with the strongest psychometric properties (reliability and validity). If the instrument is not in the public domain, send an e-mail to the author/creator of the instrument to ask for permission to use it in your study. Also request scoring guidelines from the author so you can correctly calculate the variables of interest.
If using archival data, allow yourself plenty of time to identify and gain access to an appropriate data set. The most important thing to make sure of is that the data set contains all of the variables that you need to analyze to answer your research questions. Sometimes there is extensive paperwork that is necessary to complete when utilizing a secondary data source. Keep track of all e-mail permissions and paperwork in case they are requested from the IRB. Stay in constant contact with your committee during the process and let them know if you encounter any roadblocks.
Whether you decide to collect data yourself or use archival data, planning your data collection procedures as early as possible will help you avoid delays later in the process.
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