The term is used in two different ways, and it helps to be clear which one is meant.
Scientific share of voice measures how much of the published and presented research in a therapy area concerns your product compared with its competitors. It is usually counted by publications and congress abstracts, sometimes weighted by journal or by congress, and broken down by topic, region or time. Publications and medical strategy teams use it to see where the company’s research is well represented and where competitors are dominating the conversation.
Promotional share of voice measures a brand’s share of promotional activity in its market: sales calls, advertising, events or spend. Marketing teams use it to judge their presence relative to competitors.
The two should be kept separate. Scientific share of voice is a medical measure and informs publication strategy. Promotional share of voice is a commercial one.
Volume is not the same as influence. A handful of papers in leading journals can matter more than dozens of small studies, and a high share of voice built on unfavorable results is not a win. Most teams therefore look at share of voice alongside what the publications actually say and where they appeared.