MIDTERM 2 èver 1è. Name. 2. You must show your work and explain your answer in order to receive credit.

Transcription

1 MIDTERM 2 èver 1è STA 110E Thursday, April 11, Notes: TA: Anand Krishna Heather Brunelle 1. This is an open book and open notes exam. Name 2. You must show your work and explain your answer in order to receive credit. 3. The exam has 6 problems. 4. The exam carries 100 points. 5. The points assigned to each problem are indicated at the beginning of that problem. Use them to plan your time. You have 75minutes to ænish. Problem Speed I Singers D&S Ask Speed II Demand Total Score è15 è20 è15 è15 è20 è15

2 1. ë15 ptsë Comparisons of typing speeds. èaè Ten candidates are selected at random and their typing speeds are measured prior to a short typing course èx 1 è. After the course typing speeds are measured again èx 2 è. The results are given in the table below: Candidate Before èx 1 è After èx 2 è æ Test the hypothesis that the course is useful at the level æ =5è: èbè Assume now that the same measurements X 1 and X 2 are obtained from the subjects selected from two independent groups. From the group of candidates that did not attend the course 10 subjects are selected at random èmeasurements given in the X 1 -rowè. From the group of candidates that took the course 10 are selected at random, as well, and the measurements given in the X 2 -row are obtained. æ Test the hypothesis that the course is useful at the level æ =5è: Assume that the population variances èfor the scoresè are the same. æ Comment on the ændings in èaè and èbè. èone paragraph max.è Help yourself: r çx 1 =52:5; X2 ç èn =57:0; s 1 =10:43; s 2 =10:79;s X2,X 1 =8:91;s p = 1,1ès 2 1 +èn 2,1ès 2 2 n 1 +n 2 =,2 10:61; t 18;0:05 =1:734; t 19;0:05 =1:729; t 18;0:025 =2:101; t 9;0:05 =1:833; t 9;0:025 =2:262: 2

3 ë20 ptsë Do singers of diæerent voice parts have diæerent heights? The observations were made in 1979 on heights èin inchesè of male singers of the NY Choral Society. 1 voice tenor 1: tenor 2: bass 1: bass 2: MTB é oneway c1 c2; SUBCé tukey. ANALYSIS OF VARIANCE ON C1 SOURCE DF SS MS F p C ERROR TOTAL INDIVIDUAL 95 PCT CI'S FOR MEAN BASED ON POOLED STDEV LEVEL N MEAN STDEV è------* è è------* è è------*------è è *------è POOLED STDEV = Family error rate = Individual error rate = Critical value = 3.78 Intervals for ècolumn level meanè - èrow level meanè æ What test has been performed here? What are the hypotheses H 0 and H 1? æ What are general assumptions necessary for the above procedure to be valid. æ What is your decision about H 0 and H 1 at æ =0:05? æ Give the orderings of the population means according to the tukey procedure. æ Is H 0 : ç 2 = ç 4 a contrast? If yes, test it at æ =0:05: 1 Chambers et al. è1983è Graphical Methods for Data Analysis. 3

4 ë15 ptsë Drinking & Smoking Alcohol and nicotine consumption during pregnancy are believed to be associated with certain unwanted characteristics in newborn children. Since drinking and smoking behaviors may be related, it is important to understand the nature of this relationship when assessing the possible eæects of these variables on children. In one study, mothers were classiæed according to their alcohol intake prior to pregnancy recognition and their nicotine intake during pregnancy. The data are summarized in the following table. Nicotine èmgèdayè Alcohol èouncesèdayè None or more None or more The minitab output table from the procedure CHISQ is given below: C1 C2 C3 Total Total èiè What kind of test has been performed here? Explain è1-2 sentencesè. èiiè Express the hypotheses H 0 and H 1 in terms of the problem. èiiiè Find the missing number in the cell è1,1è. èivè The ç 2 statistic in this output is Perform the test èfrom èièè at æ =0:05 and state your decision. 2 Data taken from A. P. Streissguth et al., ëintrauterine alcohol and nicotine exposure: attention and reaction time in 4-year-old children," Developmental Psychology, 20 è1984è, pp

5 ë15 ptsë When to ask? A researcher is studying the eæect on learning of inserting questions into instructional materials. There is some doubt whether these questions would be more eæective preceding or following the passage about which the question is posed. In addition, the researcher wonders if the eæect of the position of the question is the same for the factual questions and for questions that require the learner to compose a thoughtful and original response. A group of twenty-four students is split at random into four groups of six student each. One group is assigned to each of the four combinations of factor B, ëposition of question èbefore versus after the passageè," and factor A, ëtype of question èfactual versus thoughtprovokingè." After ten hours of studying under these conditions, the twenty four students are given a æfty-item test on the content of the instructional materials. The following test scores are obtained. MTB é anova B 1 B A A score = position type Factor Type Levels Values position fixed type fixed Analysis of Variance for score Source DF SS MS F position type position*type Error Total æ Complete the ANOVA table. æ Test the signiæcance of the interaction term in the model. Use æ = 5è. æ Can you test for the signiæcance of the factors A and B? Comment. 5

6 ë20 ptsë Speed Limits and Traæc Fatalities. The following table gives the speed limits èslè in 14 countries and traæc fatalities ètfè per 100,000,000 driver miles 3. MTB é regress c2 1 c1; SUBCé predict 80. The regression equation is TF = SL Country SL TF Country SL TF Italy France Hungary Belgium Portugal Britain Spain Denmark Netherlands Greece Japan Norway Poland US Predictor Coef Stdev t-ratio p Constant SL s = R-sq = 9.2è R-sqèadjè = 1.7è Analysis of Variance SOURCE DF SS MS F p Regression Error Total Fit Stdev.Fit 95è C.I. 95è P.I è 5.76, 16.05è è -1.73, 23.54è æ Comment on the output. How good is predictability of the model? æ Test H 0 : æ 0 =,10 versus the two sided alternative. Use æ =0:05: æ What is the 98è CI for the intercept æ 1? æ What is the 90è CI for the mean response for SL=80? 3 West Germany with TF=7.9 has no speed limit! 6

7 ë15 ptsë Modeling the demand function. From the Economic Report of the President, 1987 the following èpartialè table is obtained: G PG I PNC PUC PPT PD PN PS YR where Variable G PG I PNC PUC PPT PD PN PS YR Total gasoline consumption è10s mill 1967 gasoline-doll.è Price index for gasoline Per capita real disposable index Price index for new cars Price index for used cars Price index for public transportation Aggregate price for durable goods Aggregate prices for non-durable goods Aggregate prices for consumer services Normalized year èsince 1900è The goal is to model the total gasoline consumption ègè using other variables as predictors. æ From the breg procedure output propose your favorite model. Give an explanation for your choice è2-3 sentencesè. MTB é breg c1 9 c2-c10 Best Subsets Regression of G P P P Adj. P N U P P P P Y Vars R-sq R-sq C-p s G I C C T D N S R X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X 7

8 æ The full model is given below. Comment on the output. The regression equation is G = PG I PNC PUC PPT PD PN PS YR Continue? y Predictor Coef Stdev t-ratio p VIF Constant PG I PNC PUC PPT PD PN PS YR s = R-sq = 99.9è R-sqèadjè = 99.8è Analysis of Variance SOURCE DF SS MS F p Regression Error Total æ Test H 0 : æ PUC =,20 at æ =0:01: 8