Does Dr. Chase really come up with more correct diagnoses than anyone else?

Yes, I believe Chase comes up with more correct diagnoses than any other supporting character.

Firstly, this is obviously a very difficult question to answer. As discussed in the comments, how do we know who made a diagnosis? For example:

• Sometimes the entire team take part in an exploratory procedure where something is discovered. Who gets credit? The first person to call the name of the disease out? Or the person who actually finds it?
• Often ideas are brainstormed at the start of an episode. These ideas may cover anywhere from two - twenty possible illnesses. If one of those turns out to be correct, do we give credit to whoever first threw it out, or whoever actually demonstrated the victim suffered from it?
• Illnesses can be identified at a high level, but not understood at a low level. For example, it might be suggested a patient has cancer. Is that enough to claim the diagnosis? Do they need to have pinpointed where and how?
• Sometimes a diagnosis is identified, but it's not understood. Later, it is discovered a much more minor illness caused the onset of the first illness. So the first illness is more serious, but the second was the focus of the episode - so who gets credit here. The diagnoser of the serious illness, or of the secondary, less serious (and often psychological) illness?
  • Some episodes all the solutions are written up at the start on a whiteboard, and crossed off one by one. No one speaks, but someone writes them all (as the possible solutions are obvious to everyone). Who gets credit here? The person doing the writing? Or the team?

These are just some of the many, many difficulties inherent in trying to understand who is the most successful diagnoser in the team.

Despite this, I've tried to do this and my results suggest Chase is indeed the second most successful member of the team, behind House.

Methodology

There are eight seasons worth of content. That is obviously a lot. On top of that, it would be incredibly time consuming to go through each individual episode to try and pinpoint this information. Doing so would make this answer perfect, but I doubt anyone has time to do this, unless they're going on a House binge.

Instead, I chose to use the House Wiki. It has a very handy list of medical diagnoses which details what every patient, in every episode, what suffering from.

I then opened up every single episode description and read through to understand who the first person to claim the illness in the episode was:

• In a very few episodes it's unclear, so I labelled the diagnoser as "Team".
• In most, it's a clear win for House.
• In quite a few others, one of the doctors claims it early and their suspicions are confirmed later. In these cases I gave them credit, as they had initially suggested it.
• Often they suggested a general disease (e.g. cancer, or meningitis) and the answer was a subset of these. In these cases, I gave credit to the person who came up with the subset (usually House).

To understand who was most successful, I compiled a spreadsheet (a copy of which I've hosted on Google Docs). This cross references every season/episode/patient/disease with their diagnoser.

Results:

This graphs shows the Total # of Diagnoses made by every character across the entire eight seasons:

_{(Note: Please open to view it in full size)}

As can be seen, the results (in order) are:

1. House: 117
2. Chase: 20
3. Team (i.e. more than one person appeared to come up with the diagnosis at the same time): 13
4. Foreman: 9
5. Hadley ("13"): 9
6. Cameron: 6
7. Taub: 5
8. Wilson: 2
9. Adams: 2
10. Kutner: 2
11. Park: 1
12. Volakis: 1
13. Cuddy: 1
14. Masters: 1

So this would indeed suggest that Chase, by a comfortable margin, is the second best diagnoser after House.

If interested, we can look at the same results, broken down season by season:

_{(Note: Please open to view it in full size)}

House is top every season, but the second best diagnoser each season is as follows:

1. Season 1: Team: 4
2. Season 2: Tie - Chase: 3 / Team: 3
3. Season 3: Chase: 5
4. Season 4: Tie - Hadley: 2 / Kutner: 2
5. Season 5: Tie - Cameron: 2 / Hadley: 2
6. Season 6: Foreman: 3
7. Season 7: Team: 4
8. Season 8: Chase: 4

Of course, it's important to note that simply having the most diagnoses doesn't make him the best doctor. Cameron has just a single diagnosis in Season 1. Foreman has none. But they were instrumental that season, helping House out, performing valuable work (and breaking and entering) and were involved in every episode. It just appears as if they haven't done as much, as the final diagnosis didn't originate with them.

Accuracy

I will quickly repeat that this has come from a Wikipedia page and a basic study of data generated within that Wikipedia page. I'm sure it's not 100% accurate and I'm sure there will be at least a few mistakes.

However, it seems a good indicator and given Chase's clear margin of second place, I'd be confident saying your initial question was correct.

Conclusion:

With all the results in, and even accounting for the fact some of this information may be incorrect, it seems very likely Chase does in fact come up with the correct diagnosis more than any other supporting character (with House obviously dominating the diagnosis table).

Edit:

@Anthony Grist posted the following comment below:

It might be interesting to see it as a percentage of episodes they appear in as part of House's team, since I have a feeling Chase also had the most opportunities to make the correct diagnosis. In terms of raw numbers he might come second, but his actual success rate could be a lot worse than other team members who appeared in fewer seasons.

This was a really interesting idea, so I decided to plot this as well.

I used IMDB for a full list of cast credits for the show. This shows the following:

• House: 176 episodes
• "Team": 176 episodes
• Foreman: 174 episodes
• Wilson: 174 episodes
• Chase: 171 episodes
• Cuddy: 153 episodes
• Cameron: 130 episodes
• Taub: 96 episodes
• Hadley: 81 episodes
• Kutner: 37 episodes
• Adams: 21 episodes
• Park: 21 episodes
• Volakis: 18 episodes
• Masters: 15 episodes

I then updated the spreadsheet changes are on Google Spreadsheet as well with this information, cross referenced it with the number of diagnoses made per character and calculated the character's overall diagnosis success rate. This reveals the following:

So House leads the way, with the correct diagnosis in 66.48% of all his episodes.

Chase is still in second plac,e but it's very, very close. He made the correct diagnosis in 11.70% of his episodes, whilst Hadley is in third place, with the correct diagnosis in 11.11% of her episodes.

The following graph shows the same information, but includes the number of episodes each character starred in, with a trendline indicating success rate. Note the big drop off after House, and how close Chase and Hadley are.