Model Trendline Linear 3Factor Excel 2013 1

byMilo Schield

Member: International Statistical InstituteUS Rep: International Statistical Literacy ProjectDirector, W. M. Keck Statistical Literacy Project

Slides at: www.StatLit.org/pdf/Model-Trendline-Linear-3Factor-Excel2013-6up.pdf

Model using Trendline Linear 3Factor in Excel 2013

Model Trendline Linear 3Factor Excel 2013 2

Goal: Summarize association before/after control for Gender

1. Generate six XY charts as shown. No writing. 2. Show linear trendline, regression and R2 as shown.

Use XL1 (Pulse.xls) data set. Subjects are college students. Pulse1 is their resting pulse.

For details on using Excel Chart Trendline to build a model, see www.StatLit.org/pdf/Model-Trendline-Linear-Excel2013-6up.pdf

Model Trendline Linear 3Factor Excel 2013 3

#1

.Weight vs Height

y = 5.0918x - 204.74R2 = 0.616

100

140

180

220

60 64 68 72

Height

Wei

ght

Model Trendline Linear 3Factor Excel 2013 4

#2

.Rest Pulse vs. Height

y = -0.6372x + 116.65R2 = 0.0449

40

60

80

100

60 64 68 72 76

Height

Res

t Pul

se

Model Trendline Linear 3Factor Excel 2013 5

#3

.Weight by Gender

y = 34.463x + 123.8R2 = 0.5022

90

130

170

210

250

0 0.2 0.4 0.6 0.8 1

Female=0; Male=1

Wei

ght

Model Trendline Linear 3Factor Excel 2013 6

#4. Height by Gender

y = 5.3544x + 65.4R2 = 0.5102

60

65

70

75

0 0.2 0.4 0.6 0.8 1Female=0; Male=1

Hei

ght

Model Trendline Linear 3Factor Excel 2013 7

Need separate series for Men and for Women

Step 1. Copy data to a new sheet. Sort entire dataset by MALE

Step 2. Copy sorted data from A:H to J:Q.Change headings to distinguish M vs. F.

Step 3. Delete guys from gals series (Male=0);delete gals from guys series (Male=1).

Step 4. Use separated cols for graphs 5 and 6.

Model Trendline Linear 3Factor Excel 2013 8

Move data into separate series (separate columns) by Gender

Women:Min(Weight-F) = 95#Max(Weight-F) = 150#

Min(Weight-M) = 123#Max(Weight-M) = 215#Men:

Model Trendline Linear 3Factor Excel 2013 9

#5

.

Model Trendline Linear 3Factor Excel 2013 10

#6

.Rest Pulse vs. Height by Gender

Female onlyy = -0.4837x + 108.49

R2 = 0.0114

Male-onlyy = 0.2112x + 55.478

R2 = 0.003

40

60

80

100

60 64 68 72 76

Height

Res

t Pul

se

Model Trendline Linear 3Factor Excel 2013 11

Results in words

#1 As height increases by 1 inch, • weight increases by 5.1 pounds (R-squared = 62%)• rest pulse decreases by 0.64 bpm (R-squared = 5%)

#3W For women, as height increases by 1 inch, • weight increases by 2.6 pounds (R-squared = 24%)• rest pulse decreases by 0.48 bpm (R-squared = 1%)

#3M For men, as height increases by 1 inch, • weight increases by 4.4 pounds (R-squared = 36%)• rest pulse INCREASES by 0.21 bpm (R2 = 0.3%)

Model Trendline Linear 3Factor Excel 2013 12

Conclusion

Difference in gender explains part of the association between height and related variables such as weight and resting pulse.

Failure to take into account gender can result in:• associations that are spurious. • associations that reverse• associations that increase or decrease.Moral: What you take into account matters!