To determine whether to conduct a tertiary study, it is generally recommended that there be at least two systematic reviews on the topic. This allows for comparing findings and methodologies, which provides a clearer understanding of the existing evidence. If there are conflicting results, or if the systematic reviews cover different aspects of the topic, a tertiary study may be justified to further synthesize the information.

You know, that's actually a really interesting methodological question that I think doesn't have a clear-cut answer. From what I've seen, there's no magic number of systematic reviews that automatically triggers "time for a tertiary study." I think the decision is much more nuanced than just counting existing SLRs.

Kitchenham's guidance is pretty vague on this specific point, which leaves researchers in a bit of a gray area. In practice, I'd say quality matters as much as quantity here. I've seen valuable tertiary studies built on as few as 3-4 high-quality systematic reviews if they cover complementary aspects of a topic. But I've also seen situations where even with 10+ existing reviews, a new SLR made more sense because the existing ones were too narrow, outdated, or methodologically weak.

What I typically recommend is looking beyond just the raw number and asking:

• Do the existing SLRs collectively cover the scope of what you're interested in?
• Are they recent enough to include current research?
• Do they use consistent or comparable methodologies that would allow meaningful synthesis?
• Would aggregating their findings actually provide new insights?

II had never thought about it, for systematic reviews it is usually 3... and I am actually planning to conduct an umbrella review... (laughs), it was good because it made me reflect more about it. In my umbrella review, I have 6 or 7 systematic reviews, but from what I am seeing, it will probably be a bit challenging because the data are somewhat incongruent.