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Describing

Describing. Type of data FETP India. Competency to be gained from this lecture. Identify the different types of data to use appropriate methods to describe their distribution. Key issues. Qualitative data Quantitative data Distribution. Data: A definition. Set of related numbers

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Describing

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  1. Describing Type of dataFETP India

  2. Competency to be gained from this lecture Identify the different types of data to use appropriate methods to describe their distribution

  3. Key issues • Qualitative data • Quantitative data • Distribution

  4. Data: A definition • Set of related numbers • Raw material for statistics • Example: • Temperature of a patient over time • Date of onset of patients Data

  5. Epidemiological process • We want to describe a population • We collect data • We analyze data into information • “Data reduction” • We interpret the information • We use the information for decision making Data

  6. Types of data • Qualitative data • No magnitude / size • Classified by counting the units that have the same attribute • Types: • Binary • Nominal • Ordinal • Quantitative data Qualitative

  7. Qualitative, binary data • The variable can only take two values • 1, 0 • Yes, No • Example: • Sex • Male, female • Female sex • Yes, No Qualitative

  8. REC SEX --- ---- 1 M 2 M 3 M 4 F 5 M 6 F 7 F 8 M 9 M 10 M 11 F 12 M 13 M 14 M 15 F 16 F 17 F 18 M 19 M 20 M 21 F 22 M 23 M 24 F 25 M 26 M 27 M 28 F 29 M 30 M Frequency distribution for a qualitative binary variable Qualitative

  9. Using a pie chart to display qualitative binary variable Qualitative Distribution of cases by sex

  10. Qualitative, nominal data • The variable can take more than two values • Any value • The information fits into one of the categories • The categories cannot be ranked • Example: • Nationality • Language spoken • Blood group Qualitative

  11. REC NATION --- ------- Frequency distribution for a qualitative nominal variable 1 JORDAN 2 YEMEN 3 IRAN 4 JORDAN 5 YEMEN 6 JORDAN 7 YEMEN 8 TCHAD 9 SUDAN 10 IRAN 11 YEMEN 12 IRAN 13 JORDAN 14 SUDAN 15 IRAN 16 SUDAN 17 JORDAN 18 SUDAN 19 IRAN 20 YEMEN 21 SUDAN 22 YEMEN 23 SUDAN 24 IRAN 25 YEMEN 26 YEMEN 27 YEMEN 28 SUDAN 29 YEMEN 30 SUDAN

  12. Using a horizontal bar chart to display qualitative nominal variable Qualitative Distribution of cases by nationality

  13. Qualitative, ordinal data • The variable can only take a number of value than can be ranked through some gradient • Example: • Severity • Mild, moderate, severe • Vaccination status • Unvaccinated, partially vaccinated, fully vaccinated Qualitative

  14. REC Status --- ------- 1 1 2 1 3 2 4 2 5 1 6 2 7 1 8 2 9 3 10 2 11 1 12 3 13 1 14 3 15 1 16 3 17 1 18 1 19 3 20 1 21 1 22 2 23 1 24 2 25 2 26 1 27 2 28 3 29 2 30 2 Frequency distribution for a qualitative ordinal variable Clinical status: 1: Mild; 2 : Moderate; 3 : Severe

  15. Using a vertical bar chart to display qualitative ordinal variable Qualitative Distribution of cases by severity

  16. Key issues • Qualitative data • Quantitative data • We are not simply counting • We are also measuring • Discrete • Continuous Quantitative

  17. Quantitative, discrete data • Values are distinct and separated • Normally, values have no decimals • Example: • Number of sexual partners • Parity • Number of persons who died from measles Quantitative

  18. REC CHILDREN --- ------- 1 1 2 2 3 5 4 6 5 3 6 4 7 1 8 1 9 2 10 3 11 1 12 2 13 7 14 3 15 4 16 2 17 1 18 1 19 1 20 1 21 2 22 3 23 1 24 4 25 2 26 1 27 6 28 4 29 3 30 1 Frequency distribution for a quantitative, discrete data

  19. Using a histogram to display a discrete quantitative variable Quantitative Distribution of households by number of children

  20. Quantitative, continuous data • Continuous variable • Can assume continuous uninterrupted range of values • Values may have decimals • Example: • Weight • Height • Hb level • What about temperature? Quantitative

  21. REC WEIGHT --- ------ 1 10.5 2 23.7 3 21.8 4 33.1 5 38.0 6 34.5 7 38.5 8 38.4 9 30.1 10 34.7 11 37.9 12 38.0 13 39.2 14 30.1 15 43.2 16 45.7 17 40.4 18 56.4 19 55.1 20 55.4 21 66.7 22 82.9 23 109.7 24 120.2 25 10.4 26 10.8 27 25.5 28 20.2 29 27.3 30 38.7 Frequency distribution for a continuous quantitative variable: The tally mark

  22. REC WEIGHT --- ------ 1 10.5 2 23.7 3 21.8 4 33.1 5 38.0 6 34.5 7 38.5 8 38.4 9 30.1 10 34.7 11 37.9 12 38.0 13 39.2 14 30.1 15 43.2 16 45.7 17 40.4 18 56.4 19 55.1 20 55.4 21 66.7 22 82.9 23 109.7 24 120.2 25 10.4 26 10.8 27 25.5 28 20.2 29 27.3 30 38.7 Frequency distribution for a continuous quantitative variable, after aggregation

  23. Using a histogram to display a frequency distribution for a continuous quantitative variable, after aggregation Quantitative Distribution of cases by weight

  24. Series of 100 values of a quantiative variable 87.0 84.0 51.1 64.9 71.5 88.8 62.7 14.2 87.0 44.7 48.9 27.8 88.3 39.9 11.1 64.0 31.4 32.6 73.4 34.8 89.7 56.1 37.9 67.5 38.3 32.6 33.1 52.0 62.9 39.5 44.6 56.6 82.1 70.3 83.6 34.3 78.7 52.1 63.1 82.4 50.2 43.0 16.6 78.2 72.7 11.1 49.7 32.6 49.4 79.1 18.9 64.7 37.1 74.2 88.9 59.7 82.5 69.3 81.5 72.3 61.9 34.9 48.1 18.7 54.9 46.4 58.9 39.4 66.9 47.9 40.9 74.9 31.1 55.8 57.6 37.6 23.3 44.4 21.8 81.6 21.6 75.7 35.9 33.9 24.6 77.2 30.0 48.1 18.7 67.6 52.3 24.3 48.9 76.3 43.2 Quantitative 17.3 43.9 76.2 45.0 55.7

  25. Tabular and graphic representation of a distribution Values Frequency 0-9 0 10-19 8 20-29 7 30-39 18 40-49 16 50-59 13 60-69 11 70-79 14 80-89 13 90-99 0 Total 100 Distribution

  26. Describing a distribution Position Dispersion

  27. Summary Qualitative Binary Nominal Ordinal Sex Nationality Status   M Yemen Mild M Jordan Moderate F Yemen Severe M Jordan Mild F Sudan Moderate F Yemen Mild M Sudan Moderate M Iran Severe F Jordan Severe M Iran Mild F Yemen Moderate F Sudan Moderate M Iran Mild M Yemen Severe M Jordan Severe F Jordan Moderate M Iran Mild F Sudan Mild M Yemen Mild Quantitative Discrete Continuous Children Weight 1 56.4 1 47.8 2 59.9 3 13.1 1 25.7 1 23.0 2 30.0 3 13.7 2 15.4 2 52.5 1 26.6 1 38.2 1 59.0 2 57.9 2 19.6 3 31.7 2 15.1 3 33.9 1 45.6

  28. Data type in computer software Avoid free field variables difficult to analyze

  29. Exercise • Consider the class • Describe the frequency distribution of the following variable: • Sex • State of origin • Involvement in surveillance to date (None, partial, full time) • Completed numbers of years in service • Height in cm

  30. Take home messages • Qualitative data can be binary, nominal or ordinal • Quantitative data can be discrete or continuous • Distribution can be described with a table or a graph

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