A beautiful post by Dr. Atiq Rehman about control variables is a must-read.
If you investigate what brings flavor to Biryani, you can cover all the important elements in one write-up, resulting in a single paper. However, if you want to write multiple papers from the same problem, you could do it like this:
Effect of Basmati rice on Biryani
Effect of ordinary rice on Biryani
Effect of iodized salt on Biryani
Effect of Dalda cooking oil on Biryani
Effect of Tullo cooking oil on Biryani
What makes a good Biryani: a comparative analysis of Tullo and Dalda cooking oil
Effect of black pepper on Biryani
Effect of red chili on Biryani
The appropriate time for cooking a Biryani
In this way, you can choose hundreds of titles for which you can write separate papers. Each paper could be justified by stating that 'no one earlier has tested the effect of red chili on Biryani.' However, this type of analysis is strictly conditional on 'all other things remain the same' (ceteris paribus). If you analyze the effect of red chili on Biryani but the amount of salt changes in your recipe, can you conclude something reasonable about your research problem?
Think of economic growth in a similar way. Growth is much more complex than the recipe of a good Biryani. Can you analyze the effect of a single variable, such as FDI, in isolation without considering ceteris paribus or without controlling for the effects of other variables?
Therefore, a reasonable analytical methodology must consider control variables, even if they are not directly related to your problem. While analyzing the impact of FDI on economic growth, you cannot ignore human capital by saying, "I do not intend to analyze the effect of human capital; my task is to analyze the effect of FDI on growth."
Similar recommendations for research were given by DHSY in their seminal paper, but these recommendations were 'kept under red tape' for the broader interest of the academic community. If DHSY were followed, dozens of questions would be solved by a single paper, shortening the CVs of academics and potentially leading to a deficit in the business of academic journals.
