医学统计学ppt英文课件CHO2 description of measurement data教学幻灯片.pptVIP

（2）Percentile Percentile is a kind of position index. Direct method -decimal fraction： -integer： Example 2-7 Calculate no.5 and no. 99 percentile as below. Patients： Days in hospital： n=120，120X5%=6： Weighting method Formula： Section 3 Measures of Dispersion Range Quartile Variance and Standard Deviation Coefficient of Variation 1、???? Range The difference between the maximum and the minimum, R. 2、Quartile QR= Lower Quartile Upper Quartile 3、Variance and Standard Deviation Variance: A measure of dispersion or variability (spread), calculated by squaring the value of the standard deviation. Sample variance:  Population standard deviation Sample standard deviation Sample standard deviation can also be calculated as below： Example2-8 Calculate the standard deviation of values in table 2-1 4、???? Coefficient of Variation  Unit 4 Normal Distribution Fig.2-3.Frequencies Distribution Approaches ti Normal Distribution Description of Measurement Data Chapter 2 Approach： (1). Range : The difference between the maximum and the minimum, R. 。 (2)．Class Interval (i) : Usually divided into 10-15 groups (3)．Group： Lower limit（L）：the beginning of every group Upper limit（U）：the end of every group Group 2.30～ 2.60～ 2.90～ 3.20～ … 5.60～5.90 2.30～ 2.60～ (4)．Grouping and Counting Frequencies 2、Graph of frequency distribution 3、 Use of frequency table and graph of frequency distribution 1．Describing the type of frequencies distribution （1）Symmetric distribution ： （2） Skewed to the right distribution/ Positively skewed distribution (3) Skewed to the left distribution/ negatively skewed distribution 2．Describing the characteristic of frequencies distribution 3. Finding shadiness value 4. Convenient for next statistical analysis and management Section 2 Descriptions of Central Tendency