結果 and 効果: outcomes and effects
Compare the outcome of an event with the effect produced by an action or method.
What an event produces
結果 is read けっか and refers to the outcome of a test, investigation, or action. 「試験の結果を確認しました」 means that the speaker checked the test results, without stating whether they passed.
「結果は明日分かります」 says that the results will be known tomorrow. It does not mean that they have already been released or that they will necessarily be good.
The impact something has
効果 is read こうか and refers to the impact or efficacy of a method or measure. 「練習の効果が出てきました」 means that the effects of practice have begun to appear.
「効果を確かめます」 says that someone will check the effect. Distinguish the act of checking for an effect from a conclusion that the effect has been demonstrated.
Matching the word to the evaluation
「調査の結果、効果がないことが分かりました」 means that the investigation showed there was no effect. 結果 refers to the investigation's conclusion, while 効果 is the impact being investigated.
A good score can be a 試験の結果, while evidence that a study method helped can be described as 勉強法の効果. Do not replace every outcome with an effect; consider whether you are evaluating the method that produced it.
Do 「結果がよかった」 and 「効果があった」 mean exactly the same thing?
Show the answer and why
No. The first evaluates the outcome as good, while the second says that a method or measure had an effect. A good outcome alone does not establish the effect of a particular method.