I'm not sure if this is a run-on sentence.

Stock prices rose slightly yesterday. The TSE average up 16.9 points and the Canadian Exchange index up 3.2.

There is no run-on here, but there's definitely a fragment. The first sentence is fine. The second is not a complete sentence.

It's just missing a verb. If that were there, then it would need a comma, since it would be a compound sentence.

Just FYI, use "whether" when a choice is to be made; "if" introduces a conditional clause.

As it stands, you'd likely be sure, if it weren't a run-on sentence. If it's run-on, then you're not sure.

To determine if a sentence is a run-on, we need to check if it contains two or more independent clauses that are not properly connected. An independent clause is a group of words that can stand alone as a complete sentence.

In the sentence you provided, there are actually two independent clauses:
1. Stock prices rose slightly yesterday.
2. The TSE average was up 16.9 points and the Canadian Exchange index was up 3.2.

These two independent clauses can be considered as separate sentences. Therefore, the original sentence is indeed a run-on sentence.

To correct the run-on sentence, you can separate the two independent clauses into two separate sentences or use proper punctuation to connect the clauses. For example:

1. Stock prices rose slightly yesterday. The TSE average was up 16.9 points, and the Canadian Exchange index was up 3.2.
2. Stock prices rose slightly yesterday, with the TSE average up 16.9 points and the Canadian Exchange index up 3.2.

By using a period to separate the two independent clauses or by using a coordinating conjunction (such as "and") with a comma, you can create two grammatically correct sentences.