Final answer:
When faced with inconclusive quantitative correlations, the researcher should proceed with collecting qualitative data to gain deeper insights and a better understanding of the relationships between variables.
Step-by-step explanation:
The logical next step is to switch to qualitative data collection to better understand the context and reasons behind the observed correlation. Through qualitative methods, the researcher is able to build a richer context around the phenomena, understanding the 'why' and 'how' behind the numbers. Triangulation is a method used to corroborate findings through the use of multiple approaches, and in cases where quantitative results are inconclusive, qualitative approaches can provide crucial additional perspectives.
Hence, rather than simply collecting more quantitative data, analyzing existing data, or seeking expert opinions, it is advantageous to gather qualitative data to test predictions and dig deeper into the causative factors that may not be evident through numerical analysis alone.