2. Medical Statistics (full English class) Ji-Qian Fang School of Public Health Sun Yat-Sen University

3. Chapter 9 Statistical Analysis For Measurement Data

5. Numerical Description Central position (central tendency) Variation (measure of dispersion)

6. 2. Measures for Average (1) Arithmetic Mean Based on observed data Example: Blood sugar 6.2, 5.4, 5.7, 5.3, 6.1, 6.0, 5.8, 5.9

7. Based on frequency table

8. (2) Geometric mean Example 9-4 See Table 9-4

9. Based on raw data (3) Median Ranking the values of observation from the smallest to the largest, Median = the value in the middle Based on raw data Example 1: (7 values) 120,123,125,127,128,130,132 Median =127 Example 2: (8 values) 118,120,123,125,127,128,130,132 Median=(125+127)/2=126

10. Frequency Interval Based on Frequency Table

11. Symmetric RBC (10 /L)of 130 normal male adults in a place 3.8 4 4.2 4.4 4.6 4.8 5 5.2 5.4 5.6 5.8 RBC(10 /L) 0 5 10 15 20 25 30 Frequency

12. Positive skew Hair Mercury (ug/g) of 238 normal adults 0.5 0.9 1.3 1.7 2.1 2.5 2.9 3.3 3.7 4.1 Hg(ug/g) 0 10 20 30 40 50 60 70 Frequency

13. Think about How to calculate P 25 ? based on raw data? based on frequency table? How to calculate P 75 ? based on raw data? based on frequency table?

14. Summary 1.Mean: Suitable to symmetric distribution. 2. Geometric mean: Suitable to positive skew distribution 3. Median: Suitable to all kinds of data, but poor attribute for further analysis

15. 3. Measures for variability (1)Range Range= Maximum - Minimum Based on only two observations, it ignores the observations within the two extremes. The greater the number of observations, the greater the range is.

16. (2) Inter- quartile range Lower Quartile: 25 percentile Upper Quartile: 75 percentile Difference between two Quartiles = Upper Quartile - Lower Quartile = 13.120 – 8.083 = 5.037

18. (3)Variance and Standard Deviation The mean of squared deviation Standard deviation (SD)

19. Example 9-8 The weight of male infant 2.85,2.90, 2.96, 3.00, 3.05, 3.18 (1) (2)

20. (4)Coefficient of Variation Example 9-10 Variation of height and variation of weight