1. 1- Ratios and Rates

2. Example 1
In a class of 50 students, 30 students were from Riyadh and 20 students were from outside Riyadh.

3. 50 20 30 Total Outside Riyadh Riyadh students Number Find:
1- proportion of students from Riyadh.
Total
Outside Riyadh
Riyadh
students 50 20 30
Number
2- proportion of students from out Riyadh

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

5. 30 = 0.6 50 20 = 0.4 50 (Number of students from out Riyadh)
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

6. In a Medical Center we have: 1- 50 physicians 2- 150 nurses
Note that:
Sum of all proportions should equal 1
( ) = 1
Example 2:
In a Medical Center we have:
1- 50 physicians
nurses
technicians

7. a- Find proportion of nurses in the medical center
Number of Nurses = 150;
Total of Medical staff =
(nurses (150) + physicians (50) + technicians (100)) = 300

8. 150 = 0.50 300 proportion of nurses = (Number of nurses)
150 = 0.50
300
(Total of medical staff)

9. Total of Medical staff = 300
2- Find proportion of physicians
number of physicians = 50
Total of Medical staff = 300
(Number of physicians)
(Total of medical staff) 50
= 0.167
300

10. (Number of technicians)
proportion of technicians =
(Number of technicians)
(Total of medical staff)
100
= 0.333
300

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

12. 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

13. Percentage = proportion x 100
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

14. 1- Percentage of nurses = (150/300) x 100 = 50%
Example:
1- Percentage of nurses =
(150/300) x 100 = 50%
2- percentage of physicians:
(50 / 300 ) x 100 = 16.7%
3- percentage of technicians:
(100 / 300 ) x 100 = 33.3%

15. Ratio
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".

16. 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

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

18. 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

19. 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

20. There are 111 males for every 100 females

21. Year Males Females Sex ratio 2324 2134 1.00 2313 1.08 2271 0.99 2341
1991
2324
2134
1.00
1992
2313
2130
1.08
1993
2271
2276
0.99
1994
2341
2013
1.16
1995
2169
2096
1.03
1996
2063
2061
1997
2198
2018
1.09
1998
2339
2294
1.02
1999
2252
2122
1.06
2000
2092
2131
0.98

22. Characteristics of a Ratio:
1- Numerator is not part of denominator
2- Data should be collected over the same time period
If the percentage of smokers among university students is 20%, then the proportion of smokers is ________

23. Blood type frequency proportion percentage O 13 A 5 B 3 AB 4 Total 25
(13/ 25) = 0.52
0.52 x 100 = 52% A 5 B 3 AB 4
Total 25

24. 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.

25. no gestational diabetes with gestational diabetes
Women sample
400
100
500

26. 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___________

27. 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:

28. Population in this study is:
smoking status
King Saud University
3) Students
4) Students at KSU
The proportion of smokers is:
The percentage of smokers is:
The ratio of smokers to non-smokers is:

29. Rate:
Number of events, deaths or cases of disease per unit of population, in a particular time span.

30. 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).

31. 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.

32. 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.

33. 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.

34. 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:

35. Death rate = x k = (10,000) / (40,000) x k = 0.0025 (Deaths in a year)
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)

36. 2- Demography
Demography is usually defined as the study of human populations, their:
size
density and distribution
age and sex structure
marriage and divorce
The vital events, fertility, mortality, migration
(Demos = population).

37. Uses of census statistics
1. Planning for national development, i.e. educational, housing, manpower, health
planning, and e.t.c.
2. The allocation of resources.

38. Level of health services for the population KSA (2003)
Indicator
Rate per 10,000 population
Physicians
15.3
Dentist
1.8
Pharmacist
2.6
Nurses
32.3
Health technicians
18.5
Hospital beds
22.4
MOH hospital beds
13.5
Private hospital beds
4.4
Health centers
1.15

39. 3- The basic demographic equation

40. Suppose in a certain country at time t (1433) contains Pt persons, and 1 year later (1434) it contains Pt+1 persons. Then we can write down the following equation:
Pt+1 = Pt + Bt - Dt + It – Et

41. Where:
Bt : number of births occurring in the population between times t and t+1
Dt : number of deaths occurring in the population between times t and t+1.
It : number of immigrants between times t and t+1

42. Et : number of emigrants between times t and t+1.
Bt – Dt = natural increase.
It – Et = net migration.
A Country's population size can only change because of three types of events:
births,
deaths and
migration

43. 4- Data Sources

44. 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

45. 1- Population Censuses:
Most widely largest source of data carried in a country.
Most countries have regular censuses usually taken every 10 years.
Objectives of censuses:
1- Obtain information at regular intervals to facilitate comparisons over time
2- To improve comparability between countries.

46. In these censuses everyone resident in the country on a particular day is counted and asked to reply to various questions about:
age
sex
occupation
marital status
education
family size ….

47. Chief Characteristics of census:
1- Universal:
Complete recording of the entire population within a geographically well-defined area.
2- Individuality:
Each person must be recorded separately along with his or her traits.

48. 3- Government supervision:
It must a legal basis make it to be compulsory included and to provide the information requested.
4- Periodic:
Should be carried out at regular interval. Make it easier to check trends.

49. 5- Simultaneous:
It must be related to a single point in time, not a period, even though the enumeration itself may be spread over days or even weeks.

50. Data Collected in Censuses
Sex
Age
Relationship to head of household
House hold characteristics
Fertility
Mortality
Social characteristics
Economic characteristics
Place of residence

51. Design of census:
1- By respondents:
Respondents complete the questionnaire themselves and they mail it back, USA, or
the responsibility is shared, with the householders filling the questionnaire, and checked by the enumerator when it is collected.

52. 2- By enumerators:
The questionnaire is filled by enumerators with the help of the householder.

53. Country
Population (2010))
Saudi Arabia
27,448,000
Yemen
24,053,000
Palestine
4,120,000
Iraq
 32,961,960
Bahrain
1,262,000
Emirates
7,512,000
Oman
2,773,479
Jordon
6,187,000

54. Methods of conducting a census
1- De Facto Census
Counting people where they found, irrespective of their permanent residence.
For example, People attending hotels in Riyadh in the night of census are considered as Riyadh citizens, irrespective of whether they are living in Riyadh or not.

55. Advantages
simple and easy to apply
less expensive
b) Disadvantages:
Persons in transit may not be included
Provision of incorrect picture of the population distribution.
Vital rates may be distorted
This method is used in countries as: Saudi Arabia, England, Egypt, Iraq.

56. 2- De Jure Census
counting individuals at their legal permanent residence regardless to whether or not they are physically present at the time of the census.
It gives a true figure.
The disadvantages include
1- Expensive in time and money
2- Some individuals may be counted twice
3- Information may be incomplete

57. Types of error:
1- Incomplete coverage: An undercount may arise because whole areas are simply missed or because certain subgroups are hard to cover. Such groups include the homeless, nomads, infants, students, vagrants, seamen.
2- Response errors:
a- accidental: enumerator recording the answer given to him wrongly,

58. Respondent misunderstanding the question, not knowing the answer.
Errors of data entering.
b- Deliberate:
Respondent give wrong answer.
Someone may lie about his age,
divorce people may declare themselves to be single,
house proud may overstate the size of their house and the amenities they have.

59. Population censuses in Saudi Arabia

60. ( Ministry of Health, etc.).
2- Vital registration
Usually there are specialized departments, collecting such data
( Ministry of Health, etc.).
In many countries, it is usually a legal requirement to register the birth, of every child, marriage, divorce, and each death.

61. Some details may be collected, for example:
Birth: date of birth, place of birth, sex of child, name of child’s parents, occupation of child parents.
Marriage: Date of marriage, place of marriage, names of bride and groom, ages of bride and groom, previous marital status of bride and groom, occupation of bride and groom.

62. Deaths: Date of death, place of death, sex of deceased, age of deceased at death, cause of death.
The registration of migration is less wide spread. Some countries have systems of continuous registration.

63. Net migration in these countries may be estimated by:
Pt+1 - Pt - Bt + Dt
It – Et =
3- Surveys
Gaps in the data provided by censuses and vital registration can be filled by carrying out special surveys to elicit out the particular information required.

64. Advantage of sample surveys:
1- It reduces cost compared to complete enumeration.
2- can be organized and executed relatively quickly.
3- can gather more information compared to census.
Disadvantage:
1- sampling errors.

65. Surveys provided data of interest may be divided into two types:
1- prospective studies:
Involves first carrying out a normal census-type survey, which acts as a baseline, followed by repeated visits to check for and record subsequent events.
The length of visits between intervals varies.

66. The interval will be three to four months, maintained for two or three years.
Main problems:
1- Difficulties to recontact.
2- Large population which has to be covered if sufficient events which has to be recorded.
3- The high cost.
4- Difficulty of maintaining such a system for so long.

67. 2- Retrospective surveys:
a sample of people is interviewed at a single point in time, and asked questions about events which happened in the past:
Total children born alive.
numbers living at home, away and dead
Time since last birth
Contraceptive use