To effectively refine your search and manage the information for your thesis on the impact of digital literacy on secondary education outcomes in Pretoria, you should:
Utilise Boolean operators to combine search terms and exclude irrelevant topics, focusing your search on "digital literacy AND secondary education outcomes NOT higher education."
This strategy allows you to narrow down your search results significantly by clearly defining the focus of your research. It helps in filtering out irrelevant studies that do not pertain specifically to your topic, making it easier to manage the subsequent data.
The other strategies suggested, such as sticking only to local sources, changing your thesis topic, or including all topics related to education as sub-topics, could either limit your research scope too much or lead to an overwhelming amount of information, neither of which would effectively address the issue of managing the data.