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Data presentation Tables, graphs and maps

Data presentation Tables, graphs and maps. Integrated Disease Surveillance Programme (IDSP) district surveillance officers (DSO) course. Outline of the session. Analogical versus digital information Tables Graphs Maps. Communicating quantitative information.

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Data presentation Tables, graphs and maps

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  1. Data presentation Tables, graphs and maps Integrated Disease Surveillance Programme (IDSP) district surveillance officers (DSO) course

  2. Outline of the session • Analogical versus digital information • Tables • Graphs • Maps 2

  3. Communicating quantitative information • Analogical communication: Graphs • Less precise • More graphic • Provides overall understanding • Digital communication: Tables • Precise • Numeric • Provides detailed and exact description 7:00 am Digital and analogical information 3

  4. Cases of monkeypox by month of onset, Katako-Kombe, Zaire, 1996-1997 30 Example: Analogical display of information (Graph) 25 Secondary cases Number of cases 20 Primary cases 15 10 5 0 Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb 1996 1997 Month of onset Digital and analogical information 4 WHO-CDC

  5. Cases of Monkeypox by month of onset, Katako-Kombe, Zaire, 1996-1997 Example: Digital display of information (Table) Digital and analogical information 5

  6. Tables • Presentation of detailed analyzed data • Do not present raw data • E.g., lists • Present analyzed data with summary statistics Tables 6

  7. Typical table layout with components Title Column headings Data Row headings Footnotes 7

  8. How to make sure that the cells of the table are understandable without referral to other material • Title • Time, Place and Person information • Any measurement found in all columns • Row and column headings • Content of the row or column • Any modifier applied to all cells of a row or column • Unit of measurement (Abbreviations, if necessary) • Footnotes • Clarify potential ambiguities • Explain abbreviations, symbols, codes • Note exclusions • Mention data source Tables 8

  9. Selected suggestions for data arrangement in tables • Summarize rows and columns • Compare numbers in columns • Arrange key data by magnitude • Align numbers by decimal Tables 9

  10. Summary of the rows Summary of the columns 1. Summarize rows and columns Summarize rows and columns with totals, averages or other statistics Tables 10

  11. 1st improvement: Right-justify numbers vertically 2nd improvement: Sort numbers 23 27 34 42 42 75 87 98 109 114 23 42 34 109 87 42 27 98 114 75 2. Compare numbers in columns Difficult to compare numbers in rows Compare numbers in columns 23 42 34 109 87 42 27 98 114 75 Tables 11

  12. 3. Arrange key data by magnitude Organize data by magnitude Which is the most important column you would use to sort the table? Tables 12

  13. 4. Align numbers by decimal Align columns by decimal Keeping the zeros or not is a question of personal style 23 42 34 10.9 8.7 42 27 9.8 114 75 23.0 42.0 34.0 10.9 8.7 42.0 27.0 9.8 114.0 75.0 Tables 13 Difficult to compare numbers in rows

  14. Example of one way table: Data tabulated by one variable Age distribution of a sample of 100 villagers Tables 14

  15. Example of two way table: Data tabulated by two variable Age and sex distribution of a sample of 100 villagers Tables 15

  16. Classical table of incidence by age and sex Incidence of cholera by age and sex, Kachua, West Bengal, India, 2004 16

  17. Use one graph to get one general idea across • Don’t use a graph if there is nothing to say • Frame the idea to communicate • Identify the graph that matches this idea • Eliminate unnecessary information • If there are two ideas, use two graphs • Add a title with time, place and person information Graphs 17

  18. Proportion of eligible patients whose blood slides were examined for malaria, Dhenkanal district, Orissa, 1996-2002 16 14 12 10 Proportion (%) 8 Is the graph useful? 6 4 2 0 1996 1997 1998 1999 2000 2001 2002 Years Graphs 18

  19. Keep the ink-to-data ratio low • All elements on a graph must be justified • Eliminate distracting, non-essential elements • Secondary axis • Gridlines • 3-D effects • Bordering lines • Etc… Graphs 19

  20. Dracunculiasis rates, India, 1984-2000 (High ink to data ratio) 40000 39792 35000 30950 30000 25000 23070 Number of cases 20000 17031 15000 12023 10000 7881 5000 4798 2185 0 1081 755 371 1984 60 1986 9 0 1988 0 0 1990 0 1992 1994 1996 1998 2000 Year Graphs 20

  21. Dracunculiasis rates, India, 1984-2000 (Simpler, better, low ink-to-data ratio) 45000 40000 35000 30000 25000 Number of cases 20000 15000 10000 5000 0 Graphs 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 21 Year

  22. Choosing a type of graph Graphs 22

  23. 45 40 35 30 25 20 15 10 5 0 May July July July July July May May May May April April April April April June June June June June February March March March March March August August August August August January October January October January October January October January October February February February February November December November December November December November December November December September September September September September Line graph for time series Malaria in Kurseong block, Darjeeling District, West Bengal, India, 2000-2004 Incidence of malaria Incidence of Pf malaria Incidence of malaria per 10,000 2000 2001 2002 2003 2004 Months Graphs 23

  24. Histogram to display a frequency distribution • Graphic representation of the frequency distribution of a continuous variable • Rectangles drawn in such a way that their bases lie on a linear scale representing different intervals • Areas are proportional to the frequencies of the values within each of the intervals • No spaces between columns • No scale breaks • Equal class intervals • Epidemic curve is an example of histogram with time on the x axis Graphs 24

  25. Histogram Urinary iodine excretion status, 24 N Parganas, West Bengal, India, 2004 80 60 40 Percentage 20 0 0-19.9 20-49.9 50-99.9 100-300 > 300 Urinary Iodine Excretion levels (µg/L) Graphs 25

  26. Epidemic curve Acute hepatitis by week of onset in 3 villages, Bhimtal block, Uttaranchal, India, July 2005 90 80 70 60 50 Number of cases 40 30 20 10 0 1st week 3rd week 1st week 1st week 1st week 1st week 3rd week 3rd week 3rd week 4th week 4th week 4th week 2nd week 4th week 2nd week 2nd week 2nd week May June July August September Week of onset Graphs 26

  27. Proportions of a total presenting selected characteristics • Breakdown of a total in proportions: • Pie chart • Breakdown of more than one total into proportion: • Juxtaposed bar charts cumulated to 100% Graphs 27

  28. Pie chart for the breakdown of a total in proportions Types of unintentional injuries, Tiruchirappalli, Tamil Nadu, India, 2003 • Incidence: 9.6 per 100 person-month (95% C.I. 8-11 Road 10% Minor injuries 35% Fall 32% Bites 16% Graphs Burns 28 7%

  29. Cumulated bar chart for the breakdown of more than one total in proportions Estimated and projected proportion of deaths due to non-communicable diseases, India, 1990-2010 100% 90% 80% Injuries 70% 60% Communicable Proportion (%) 50% diseases 40% Non communicable 30% diseases 20% 10% 0% 1990 2000 2010 Graphs 29 Year

  30. Comparing proportions • No logical order: Horizontal bar chart • Sort according to decreasing proportions • Logical order: Vertical bar chart Graphs 30

  31. Horizontal bar chart Causes of non vaccination as reported by the mothers, Bubaneshwar, Orissa, India, 2003 Lack of awareness Child sick Irregularity by health staff Lack of motivation Lack of time Lack of facility Lack of money 0% 20% 40% 60% 80% 100% Graphs 31 India FETP

  32. Vertical bar chart Prevalence of hypertension by age and sex, Aizawl, Mizoram, India, 2003 70 60 50 40 Male % 30 Female 20 10 0 30-39 40-49 50-59 60-69 70 + Age group (years) Graphs 32

  33. Maps • Use maps to display information by place • Do not use tables! • Two types of maps: • Spot maps • Incidence maps • Use a key • Add a title with time, place and person information Maps 33

  34. Drawing a spot map during an outbreak investigation • Rough sketch of the setting of an outbreak • One dot = One case • Other locations of potential importance are also recorded • Does not adjust for population density Maps 34

  35. Spot map - Does not adjust for population density Cholera cases by residence, Kanchrapara, N-24 Parganas, West Bengal, India, 2004 Maps 35

  36. An incidence map adjusts for population density • List the cases • Regroup cases by location for which population denominator is available • Look up census data • Divide the number of cases by the population denominator • Choose gradients of colours to represent increasing levels of prevalence Maps 36

  37. Old well used onlyin the summer Water tank filled with well water Incidence map - Adjusts for population density Cholera attack rate and water supply, Sirunavalur, Tamil Nadu, India, 2002 Attack rate by area Reddiar street 0-5% Valluvar |street 5 –10 % PL street > 10 % Main road Main road Main road Colony Centre east Muthuraja Maps 37

  38. Preparing an incidence rate map: What you will need • A hardcopy of your map • A transparency • Cello tape • Permanent markers • Computer • Drawing software • Incidence by geographical area 38

  39. Step 1: Place transparency on the hardcopy of map to draw map with permanent marker 39

  40. Step 2: Stick the transparency on the screen with cello tape and follow the guide to draw map with the mouse in a drawing software 40

  41. Step 3: Remove the transparency and edit the map in the drawing software 41

  42. Step 4: Filling the map with data • Have a table of incidence by area • Rank the areas by increasing level of incidence • Sort the areas in four groups in which there is about the same number of area • Add a fifth group if needed for incidence = 0 • Assign a colour per group • Draw the map 42

  43. Rate of disease X by country, South East Asia WHO region, 200X Yearly incidence per 100,000 0 0-19 20-49 50-99 100+

  44. Using colours in maps • The cold / warm scale • Represents violent contrasts • Increasing density in one colour • Represents increasing levels of magnitude • Complementary colours • Use equivalent intensity • Represents unrelated notions Maps 44

  45. Take home messages • Choose whether you want to represent an overall message (Analogical) or whether you want to describe detailed data (digital) • Present analyzed data in tables with summary rows and columns • Display general ideas in graphs that carry one single message • Use maps to display information by place 45

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