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MEASURES OF CENTRALITY. Last lecture summary Mode Distribution.

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Presentation on theme: "MEASURES OF CENTRALITY. Last lecture summary Mode Distribution."— Presentation transcript:

1 MEASURES OF CENTRALITY

2 Last lecture summary Mode Distribution

3 Life expectancy data

4 Minimum Sierra Leone minimum = 47.8

5 Maximum Japan maximum = 84.3

6 Life expectancy data all countries

7 Life expectancy data Egypt half larger half smaller

8 Life expectancy data Minimum = 47.8 Maximum = 83.4 Median = 73.2

9 Q Sao Tomé & Príncipe 50 (¼ way) 1 st quartile = 64.7

10 Q1 ¾ larger¼ smaller 1 st quartile = 64.7

11 Q Netherland Antilles 148 (¾ way) 3 rd quartile = 76.7

12 Q3 3 rd quartile = 76.7 ¾ smaller¼ larger

13 Life expectancy data Minimum = 47.8 Maximum = 83.4 Median = st quartile = rd quartile = 76.7

14 Box Plot

15 Box plot 1 st quartile 3 rd quartile median minimum maximum

16 Quartiles, median – how to do it? 79, 68, 88, 69, 90, 74, 87, 93, 76 Find min, max, median, Q1, Q3 in these data. Then, draw the box plot.

17

18 Another example Min. 1st Qu. Median 3rd Qu. Max , 93, 68, 84, 90, 74

19 Percentiles věk [roky]

20 Skeleton data Estimate age at death from skeletal remains Common problem in forensic anthropology Based on wear and deterioration of certain bones Measurements on 400 skeletons Two estimation methods Di Gangi et al., aspects of the first rib Suchey-Brooks, most common, pubic bone

21 400 skeletons, the estimated and the actual age of death

22 DiGangi

23 Modified boxplot Min. Q1 Median Q3 Max

24 Mean

25 Median = -13 Mean = Mean is not a robust statistic. Median is a robust statistic. Robust statistic

26 Median = -13 Mean = % trimmed mean … eliminate upper and lower 10% of data (i.e. 40 points). 10% trimmed mean = mean of 320 middle data values = Trimmed mean is more robust. Trimmed mean

27 Salary o 25 players of the American football (NY red Bulls) in median = mean = % trimmed mean =

28 MEASURES OF VARIABILITY

29 Navození atmosféry

30 QUESTION Mean1 Mean2 Mode1 Mode2 Median1 Median2

31 range (variační rozpětí) MAX - min

32 Range Range changes when we add new data into dataset Always Sometimes Never

33 Adding Mark Zuckerberg

34 Cut off data IQR, mezikvartilové rozpětí

35 Interquartile range, IQR Let’ take this quiz, answer yes ot not. 1. About 50% of the data fall within the IQR. 2. The IQR is affected by every value in the data set. 3. The IQR is not affected by outliers. 4. The mean is always between Q1 and Q Q2Q1=1 Q3=3

36 Define outlier Sample $38,946 $43,420 $49,191 $50,430 $50,557 $52,580 $53,595 $54,135 $60,181 $10,000,000 What values are outliers for this data set? 1.$60,000 2.$80,000 3.$100,000 4.$200,000

37 Problem with IQR normal bimodal uniform

38 Options for measuring variability Find the average distance between all pairs of data values. Find the average distance between each data value and either the max or the min. Find the average distance between each data value and the mean.

39 Average distance from mean Sample

40 Average distance from mean Sample

41 Average distance from mean Sample Find the average distance between each data value and the mean.

42 Preventing cancellation How can we prevent the negative and positive deviations from cancelling each out? 1. Ignore (i.e. delete) the negative sign. 2. Multiply each deviation by two. 3. Square each deviation. 4. Take absolute value of each deviation.


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