The computer records your answers during the USMLE STEP 1 and USMLE STEP 2 CK . Your answers are sent to the National Board of Medical Examiners for scoring. Your total number of correct answers are mathematically rendered into a three-digit exam score and also a two digit exam score.
Most exam scores will be in the 140-260 range. The mean score for graduates of US medical schools is 210-230, with a standard deviation of 20. The passing score is 188 on the three digit scale and 75 on the two digit scale. A score of 247 on the three point scale corresponds to 99 on the two point scale.
For USMLE Step 2- CS your ability to collect information from the patient, communication skills and your ability to put together a sensible and coherent patient note will be assessed. The result is reported as a pass or fail.
Especially if you are an IMG, you should definitely target a score of 220 and above. If you can manage a score above 240, you will have a decent shot at the speciality that you wish for. Of course there are other factors that influence a program director's decision.
A high USMLE score accomplishes one thing, it gets you an interview invitation. From there on, it entirely hinges on your interview skills and any contact you have at the residency program where you are applying. If you know someone who works there, like a current resident who can recommend you, or a faculty member who is related to you, that helps a lot. At the interview itself, the program directors and other faculty will mostly assess whether you will get along with them. And my 'getting along' it does not mean brown-nosing. It means you will fit into the system.
The US system works on the principle of responsibility from below up and authority from above down. As the lowest peon in the hierarchy, you will have significant responsibilities on your shoulders, minimal or no authority, and everyone whom you see is your boss in some form or other. You would need to be a better diplomat than the hapless UN representatives at at middle east summit. Life as a resident is incredibly stressful, you will have zero time for your family and everything else, you will be the whipping boy for the professor, the assistant professor, the nurse, the pharmacist, the patient , the patient's ex-husband and everyone else who crosses your path. The trick is to keep smiling, and not get anyone mad at you and survive those three to five years. You are not going to invent a cure for cancer while you are a resident. Your job as a resident is to survive, and not harm any patients and not get any of the faculty mad at you.
At the interview they will try to find out if you have sufficient tact, intelligence, patience and also clinical knowledge to do all that. Convince the program director that you 'enjoy' being busy and 'love' working long hours. Convince him how you are totally in love with the speciality, whether it be internal medicine or psychiatry. It does not hurt to drop hints that you are interested in clinical research, and any research projects that you have done before will be a big plus. Be prepared to discuss those projects intelligently.
But.. like they say, you can cross that bridge when you get there. Right now focus on getting a USMLE score of 240. That should be your objective. Remember, if you pass the USMLE with a low score such as 188, you can kiss all of your medical dreams permanently goodbye. If you fail the USMLE with a dismal score of 187, you are fine, because you can re-take the exam.
Program directors typically rely more on the three digit score, since the equivalence of the score remains the same regardless of the year when you tested whereas the relevance of the two digit score changes with time. For example, a score of 80 was enough to get you into an internal medicine residency fifteen or twenty years back, but right now you wont even get past the front door of a residency program with a score of 80.
Keep in mind that many program directors give more importance to step 1 than to step 2, because that is a pretty good indicator of the type of student you were when you were in medical school. Most students who did well in medical school will do really well in the step 1.
To summarize, aim high, work hard and focus on the USMLE until you ace it.