Basic Applied Statistics 200
Solutions to Midterm 1 at 11:00
-
- (iii) 5 number summary values (and boxplots) are higher for males
(except for one female high outlier)
- (iii) the box is taller for males, and IQR is 6, as opposed to 2 for
females
- (iii) the 3 high outliers are obvious
- (iii) for right skewness/high outliers, mean > median
- Five Number Summary is better in the case of skewness and/or outliers
-
- stems should be 0 (leaves 122334), 0 (leaf 5), 1 (leaves 000),
1 (leaf 5), 2 (leaves 00)
- no: the shape is skewed right
- 5 (the 7th value of 13)
- (ii) 6 [the numbers look to be about 6 away from their mean, typically]
-
- 1-.6700=.3300, or by symmetry look up z=-.44
- .0228-.0013=.0215
- -1.64 or -1.65
-
- 500 plus or minus 2(115): between 270 and 730
- x < 300 means z < -1.74; proportion is .0409
- the mean, 500
- cut-off for top 15% same as for bottom 85%: z= +1.04, so x=500+1.04(115)
=619.6
-
- heights
- (i) positive (iii) linear (v) strong
- positive square root of .830 (Rsquared) is .91
- .91 (r unaffected by change in units of measurement)
- -21.7 + (0.455)70 = 10
- 9.5 - 10 = -.5
- (iii) [the output indicates both R and X for this observation]
- (i) without that student, the points exhibit looser clustering
- (i) a random residual plot indicates a straight line alone is a good
summary
-
- males: 12/20 = .6 vs 21/42 = .5
- 21/29 = .72
- 21/62 = .34
-
- (i) an observational study; imposing a treatment of meals would be
unrealistic
- (i)
- (iii)
-
- Pitt students constitute the population
- 3 times 2 = 6
-
- (ii) treatment is chewing, so control should be not chewing
- (i) randomness avoids bias
- (i) adequate replication is another principle of good design
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