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Basic measurements in Demography

This outline provides an overview of the basic measurements used in demography, including ratio, proportion, and rate. It explains the concepts and provides examples for better understanding.

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Basic measurements in Demography

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  1. Basic measurements in Demography

  2. Outline: • Ratio • Proportion • Rate

  3. 1. Ratio • Ratio is the relationship between two numbers ( one is divided by the other). Those included in the numerator may or may not be included in the denominator • Examples: Sex Ratio: number or males/ number of females Risk Ratio: Risk of disease in one group(exposed) Risk of disease in another group ( unexposed)

  4. If "a" is one number and "b" is another; a ratio between the two is: a/b or a:b • means "so many "a" per unit of b".

  5. Example 1: In a class of 50 students, 30 students were from Riyadh and 20 students were from out Riyadh. Find ratio of students from Riyadh to students from out Riyadh R= 30 : 20 or 30/20 = 1.50

  6. Interpretation: • for every 150 students from Riyadh there are 100 students from outside Riyadh.

  7. Example 2: • Sex ratio: is simply the ratio of males to females. • This ratio is usually expressed as the number of males per 100 females. • written as: males : females

  8. Suppose we have: males = 1000; females = 900; then: sex ratio = 1000 : 900 or can also be written as: (10/9) = 1.11 Or can be written as: 111 : 100 There are 111 males for every 100 females

  9. Characteristics of a Ratio: 1- Numerator is not part of denominator except in special Ratios ( rates, proportion) 2- Data should be collected over the same time period

  10. 2. Proportion • A special ratio where a number if individuals within a defined group with the outcome of interest (numerator) is divided by the number of individuals enumerated in the population ( denominator) • The numerator is a subset of the denominator a/a+b

  11. Example • In a class of 50 students, 30 students were from Riyadh and 20 students were from outside Riyadh.

  12. Find: 1- proportion of students from Riyadh. 2- proportion of students from out Riyadh

  13. Proportion of students from Riyadh = Note that: All students in the class = 50 students from Riyadh + students from out Riyadh 30 + 20 (Number of students from Riyadh) (All students in the class)

  14. Proportion of students from Riyadh = 30 = 0.6 50 Proportion of students from out Riyadh = (Number of students from out Riyadh) (All students in the class) 20 =0.4 50

  15. Note that: • Sum of all proportions should equal 1 • (0.6 + 0.4) = 1 Example In a Medical Center we have: 1- 50 physicians 2- 150 nurses 3- 100 technicians

  16. a- Find proportion of nurses in the medical center

  17. 2- Find proportion of physicians

  18. proportion of technicians

  19. Note that: • Sum of all proportions should equal 1 • ( ) = 1

  20. Characteristics of proportion: 1- Numerator is part of denominator. 2- The value of the proportion will always be some decimal number between 0 and 1 0 ≤ P ≤ 1 3- Difficult to interpret

  21. To make the proportion easy to interpret; • we change it to percentage by multiplying by 100 Percentage = proportion x 100 • Range of values for percentage is from 0 to 100. 0 ≤ Percentage ≤ 100

  22. Example: 1- Percentage of nurses = ( ) x = % 2- percentage of physicians: ( ) x 100 = % 3- percentage of technicians: ( ) x 100 = %

  23. 3. Rate • Special ratio where a number if individuals within a defined group with the outcome if interest ( numerator) is divided by the number if individuals enumerated in the population (denominator) per unit length of time I.e. Rate is the number of persons (diseased or death) per unit of population per unit of time The numerator is a subset of the denominator = a/a+b

  24. To calculate a rate the following are needed: • defined period of time (year) • defined population (country, city) • number of events occurring during a period (number of deaths in a country during a year).

  25. The formula for calculating a rate is given by: • Rate = (a/ (a + b)) x k • Where: • a = frequency with which an event has occurred during some specified period of time, usually a year.

  26. a + b = number of persons exposed to the risk of event during the same period of time. • k = some number such as 10, 1000, 10,000. • The nominator is a component part of a denominator. • The purpose of multiplying by k is to avoid results involving very small numbers.

  27. Rates are useful for: • Comparing disease occurrence: • in different locations whose populations differ in size. • during different periods of time. • For example: • 19.5 cases of chickenpox/ 100,000 in 2001 • 135.8 cases per 100,000 in 1991.

  28. Example: • Suppose in a certain area, total number of population is 4,000,000. Suppose in a certain year 10,000 died. • If we would like to compute death rate:

  29. Death rate = • = (10,000) / (40,000) x k = 0.0025 • We can select k to be 10,000. • We expect population to be reduced by 25 for every 10,000. (Deaths in a year) x k (Total population)

  30. In order to calculate rate and ratios, data are required on both: • 1- The number of events occurring within the given time interval, and • 2- The population exposed to the risk of experiencing those events. • There are three main sources: • 1- Population censuses • 2- vital registration • 3- Surveys

  31. Exercises • If the percentage of smokers among university students is 20%, then the proportion of smokers is ________

  32. Gestational diabetes is a form of diabetes that occurs in some pregnant women during pregnancy. • In a sample of 500 pregnant women in Riyadh selected from primary health care centers with no previous history of diabetes, 100 were found to have a gestational diabetes.

  33. a- Proportion of women who were found to have gestational diabetes is: ____________ b- Percentage of women who were found to have gestational diabetes is: ____________ c- Ratio of women with gestational diabetes to women with no gestational diabetes is___________

  34. In a study on smoking status at King Saud University (KSU), a sample of 1000 students were selected. • Each student was asked whether he smokes or not. • It was found that among the students who were selected, 100 students smoke, based on this information we can say:

  35. The proportion of smokers is: • The percentage of smokers is: • The ratio of smokers to non-smokers is:

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