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Evaluating a Variable as a Proxy for another Measure: Assessing the Step Test Exercise Prescription as a Proxy for the Maximal, High- intensity Peak Oxygen.

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Presentation on theme: "Evaluating a Variable as a Proxy for another Measure: Assessing the Step Test Exercise Prescription as a Proxy for the Maximal, High- intensity Peak Oxygen."— Presentation transcript:

1 Evaluating a Variable as a Proxy for another Measure: Assessing the Step Test Exercise Prescription as a Proxy for the Maximal, High- intensity Peak Oxygen Consumption in Older Adults Jonathan D. Mahnken, Ph.D., PStat ® Associate Professor of Biostatistics The University of Kansas Medical Center Director, Data Management and Statistics Core The University of Kansas Alzheimer’s Disease Center © 2013 Jonathan D. Mahnken. All Rights Reserved.1

2 In Collaboration with…  Xueyi Chen, Ph.D.  Alexandra R. Brown, M.S.  Eric D. Vidoni, Ph.D.  Sandra A. Billinger, Ph.D. © 2013 Jonathan D. Mahnken. All Rights Reserved.2

3 Acknowledgement  The University of Kansas Alzheimer’s Disease Center (P30 AG035982) for support of the Data Management and Statistics Core  Aim 2: Provide Statistical Expertise for ADC Projects Aim 2a: Support Study Design, Oversight, and Data Analyses Aim 2b: Participate in the Preparation of Study Presentations and Publications Aim 2c: Develop Novel Statistical Methodology to Ensure Proper Interpretation of ADC Data © 2013 Jonathan D. Mahnken. All Rights Reserved.3

4 Motivating Example  KU ADC thematic focus on modifiable lifestyle risk factors and AD prevention  Maximal, high-intensity peak oxygen consumption (VO 2 peak) an important measure of fitness  Interested in whether a lower-impact, sub-maximal Step Test Exercise Prescription, or STEP, could serve as valid proxy  Less equipment required: staircase and stopwatch  Likely to facilitate better subject recruitment for AD research  Validity of STEP as a proxy for VO 2 peak in older adult population unclear © 2013 Jonathan D. Mahnken. All Rights Reserved.4

5 Statistical Definition © 2013 Jonathan D. Mahnken. All Rights Reserved.5 (Kotz and Johnson eds., 1986, p 323)

6 Valid Proxy © 2013 Jonathan D. Mahnken. All Rights Reserved.6

7 Valid Proxy (cont.) © 2013 Jonathan D. Mahnken. All Rights Reserved.7

8 Valid Proxy (cont.) © 2013 Jonathan D. Mahnken. All Rights Reserved.8

9 9

10 An Extreme Example Aside © 2013 Jonathan D. Mahnken. All Rights Reserved.10

11 Test of Unbiased Proxy © 2013 Jonathan D. Mahnken. All Rights Reserved.11

12 Linear Transformation © 2013 Jonathan D. Mahnken. All Rights Reserved.12

13 Linear Transformation (cont.) © 2013 Jonathan D. Mahnken. All Rights Reserved.13

14 Linear Transformation (cont.) © 2013 Jonathan D. Mahnken. All Rights Reserved.14

15 © 2013 Jonathan D. Mahnken. All Rights Reserved.15

16 © 2013 Jonathan D. Mahnken. All Rights Reserved.16

17 © 2013 Jonathan D. Mahnken. All Rights Reserved.17

18 Comments on Comparing the Power Functions © 2013 Jonathan D. Mahnken. All Rights Reserved.18

19 Compare Power Curves © 2013 Jonathan D. Mahnken. All Rights Reserved.19

20 © 2013 Jonathan D. Mahnken. All Rights Reserved.20

21 © 2013 Jonathan D. Mahnken. All Rights Reserved.21  Power = type I error when unbiased

22 © 2013 Jonathan D. Mahnken. All Rights Reserved.22

23 © 2013 Jonathan D. Mahnken. All Rights Reserved.23

24 © 2013 Jonathan D. Mahnken. All Rights Reserved.24

25 © 2013 Jonathan D. Mahnken. All Rights Reserved.25

26 © 2013 Jonathan D. Mahnken. All Rights Reserved.26

27 © 2013 Jonathan D. Mahnken. All Rights Reserved.27

28 © 2013 Jonathan D. Mahnken. All Rights Reserved.28

29 © 2013 Jonathan D. Mahnken. All Rights Reserved.29

30 © 2013 Jonathan D. Mahnken. All Rights Reserved.30

31 © 2013 Jonathan D. Mahnken. All Rights Reserved.31

32 © 2013 Jonathan D. Mahnken. All Rights Reserved.32

33 © 2013 Jonathan D. Mahnken. All Rights Reserved.33

34 © 2013 Jonathan D. Mahnken. All Rights Reserved.34

35 © 2013 Jonathan D. Mahnken. All Rights Reserved.35

36 Motivating Example © 2013 Jonathan D. Mahnken. All Rights Reserved.36

37 Motivating Example (cont.) © 2013 Jonathan D. Mahnken. All Rights Reserved.37

38 Motivating Example (cont.) © 2013 Jonathan D. Mahnken. All Rights Reserved.38

39 Summary and Limitations © 2013 Jonathan D. Mahnken. All Rights Reserved.39

40 Future Directions © 2013 Jonathan D. Mahnken. All Rights Reserved.40

41 References Kotz S, Johnson NL eds., Encyclopedia of Statistical Sciences, Vol. 7. John Wiley & Sons: New York, 1986. Vidoni ED, Mattlage A, Mahnken J, Burns JM, McDonough J, Billinger SA: “Validity of the Step Test for Exercise Prescription Does Not Extend to a Larger Age Range.” Journal of Aging and Physical Activity. (Accepted in 2012.) © 2013 Jonathan D. Mahnken. All Rights Reserved.41

42 I S H E D © 2013 Jonathan D. Mahnken. All Rights Reserved.42 Questions?

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