SparkToro's audience data is built from a large, continuously refreshed base of anonymized clickstream data, combined with public LinkedIn profiles. Rather than counting individual profiles, think of it as a broad, behavioral picture of where real people actually spend their attention online.
Because audiences are described by aggregating across this large pool of data, broad audiences (for example, "people who talk about marketing") draw from very large samples, while highly niche audiences draw from smaller ones. If a report returns thin results, try broadening the query. See Tips for improving your audience research.