Friday, March 14, 2008

Final Exam Recap

Well, it's finally over! Here's a recap of my random thoughts on the final exam:

  • In general, the final was harder than I expected. I'm pretty sure I did well, but it was definitely harder than the midterm and harder than I thought it would be.
  • He hit us with 10 straight questions from Chapter 12 right out of the block! I expected to ease into it. The previous quarter's final was pretty linear - starting at chapter 7, then chapter 8, etc and not hitting chapter 12 until the last questions. I knew chapter 12 would be a big chunk of the exam, but I didn't expect him to lead off with it.
  • I think we were all pretty stumped by that one question (was it 9 or 10?) that had us calculate the intercept, b0. I kept coming up with 100 for an answer, but it wasn't one of the choices. I saw Azzam go up and ask about something and figured it might be that. So I went up and asked also. I think we all breathed a sigh of relief when he made the change to the last two choices. BTW, I think he could have just changed Σ Y to be 100 and that would have made the intercept 40, which was one of the choices.
  • Probability of Type I errors? Sheesh! I didn't see that coming. The answer is that it's alpha, α.
  • I was surprised at the "regular" question that had us work out the regression from the raw data. I'm almost positive I made some arithmetic mistakes in calculating the Σ(Xi-Xbar)(Yi-Ybar) or Σ(Xi-Xbar)2 or one of the other calculations.
  • My answer for the "west nile" question was that we do not reject the null hypothesis, H0 that the average # of cases is different than 3.
  • On the last question, part A, you had to assume (or somehow know through ESP or divine vision) that the level of confidence to use is 95%. You can calculate the t-score easily enough (I think I got something like 2.414), but draw any conclusions, you need to calculate the critical value for tα/2, n-1 which requires the level of confidence.
  • I knew there would be a Durbin-Watson question on the exam! My answer for that one was that there was not evidence of autocorrelation since the DW stat was greater than dU and less than 2+dL. I'm not sure I was using the right dU because I wasn't sure if I should use α or α/2 on the DW table. I used α (which I think was 0.05).
  • As predicted, there were a few questions with Minitab output. No big surprises there.
  • In at least 2 of the questions (one multiple choice and one "regular"), he gave us the variance rather than the standard deviation. Tricky! I almost fell for that one.
  • One question asked us to determine sample size, given a confidence level, margin of error and standard deviation (or maybe variance). Using the formula, you calculate n=74.3 (something like that - not a round number). You had to know to round up, not truncate the decimal.
  • Higher confidence levels need wider intervals. You had to figure he would ask about that.
  • If p is low, H0 must go! You could use that to answer one of the multiple choice question on p-value approach in hypothesis testing.
All in all, not a terrible test. Just harder than last quarter's final, IMHO. I'm anxious to see how I did. I think he said he may have them graded by Monday. The multiple choice is easy to grade. I think he gives the "regular" questions to a Teaching Assistant. HW5 grades have not been posted to Blackboard yet.

2 comments:

lowkeydad said...

now the only question is... when is he going to get the grades back! :)

Great get-together after the test by the way, had a lot of fun.

Cemil said...

I've enjoyed your blog very much. Was following it throughout the quarter. Good luck with other classes as well...
Cemil