Medical Statistics (full English class)

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Medical Statistics (full English class). Ji-Qian Fang School of Public Health Sun Yat-Sen University. Chapter 9. Statistical Analysis For Measurement Data. Numerical Description. Central position (central tendency) Variation (measure of dispersion). 2. Measures for Average.

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### Medical Statistics (full English class)

Ji-Qian Fang

School of Public Health

Sun Yat-Sen University

Chapter 9

Statistical Analysis

For

Measurement Data

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

(2) Geometric mean
• Example 9-4 See Table 9-4
(3) Median Ranking the values of observation from the smallest to the largest, Median = the value in the middleBased 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

Based on Frequency Table

Frequency

Interval

Frequency

30

25

20

15

10

5

0

3.8

4

4.2

4.4

4.6

4.8

5

5.2

5.4

5.6

5.8

RBC(10 /L)

Symmetric

RBC (10 /L)of 130 normal male adults in a place

Frequency

70

60

50

40

30

20

10

0

0.5

0.9

1.3

1.7

2.1

2.5

2.9

3.3

3.7

4.1

Hg(ug/g)

Positive skew

Hair Mercury (ug/g) of 238 normal adults

• How to calculate P25?

based on raw data?

based on frequency table?

• How to calculate P75?

based on raw data?

based on frequency table?

Summary
• 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

3. Measures for variability
• 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.

(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

(3)Variance and Standard Deviation

The mean of squared deviation

Standard deviation (SD)

Example 9-8 The weight of male infant

2.85,2.90, 2.96, 3.00, 3.05, 3.18

(1)

(2)

(4)Coefficient of Variation

Example 9-10 Variation of height and variation of weight