Are there any numbers (estimates) for how many anime shows have been adapted from manga, light novels, visual novels, and games? How big a portion of anime gets adapted from different sources like manga, light novels, visual novels, and video games in general?
Has there ever been published a study or numbers that looked into how many anime shows have their origins in the different media and drawn a comparison between them?
Databases like myanimelist or anisearch often include the original source for each entry.
The second database also allows us to filter the entries based on the source type so we can get some numbers.
The following are rough estimates when we only consider series (overall about 4700):

Based on manga: 1620
Based on light novel: 400
Based on video game: 280
Based on visual novel: 160
Original works: 880

Not included are adaptations from other media like comics, manhua, manwha or other anime.