04/19/2023 1

APPLIED EPIDEMIOLOGY

NesidaiIntroduction Lecture 1

04/19/2023 2

Objectives

By the end of the lesson, the learner should be able to:Define epidemiologyTerminologiesSummarize the historical evolution of epidemiology (Hand out)Describe the elements of a case definition and state the effect of changing the value of any of the elementsUses of Epidemiology

04/19/2023 3

The word epidemiology comes from the Greek words epi, meaning “on or upon,” demos, meaning “people,” and logos, meaning “the study of.” Many definitions have been proposed, but the following definition captures the underlying principles and the public health spirit of epidemiology:

04/19/2023 4

“Epidemiology is the study of the

distribution and determinants of

health-related states or events in

specified populations, and the

application of this study to the

control of health problems.”

04/19/2023 5

Terminologies

Study. Epidemiology is a scientific discipline, sometimes

called “the basic science of public health.” It has, at its

foundation, sound methods of scientific inquiry.

Distribution. Epidemiology is concerned with the

frequency and pattern

04/19/2023 6

Distribution. Epidemiology is concerned with the

frequency and pattern of health events in a population.

Frequency includes not only the number of such events in a

population, but also the rate or risk of disease in the

population. The rate (number of events divided by size of

the population) is critical to epidemiologists because it

allows valid comparisons across different populations.

Pattern refers to the occurrence of health-related events by

time, place, and personal characteristics.

04/19/2023 7

Time characteristics include annual occurrence, seasonal

occurrence, and daily or even hourly occurrence during

an epidemic.

Place characteristics include geographic variation,

urban-rural differences, and location of worksites or

schools.

Personal characteristics include demographic factors

such as age, race, sex, marital status, and socioeconomic

status, as well as behaviors and environmental exposures

04/19/2023 8

This characterization of the distribution of health-

related states or events is one broad aspect of

epidemiology called descriptive epidemiology.

Descriptive epidemiology provides the What, Who,

When, and Where of health-related events.

Determinants. Epidemiology is also used to search

for causes and other factors that influence the

occurrence of health-related events. Analytic

epidemiology attempts to provide the

04/19/2023 9

Why and How of such events by

comparing groups with different rates of

disease occurrence and with differences

in demographic characteristics, genetic or

immunologic make-up, behaviors,

environmental exposures, and other so-

called potential risk factors.

04/19/2023 10

Under ideal circumstances, epidemiologic

findings provide sufficient evidence to direct

swift and effective public health control and

prevention measures

04/19/2023 11

Health-related states or events.

Originally, epidemiology was concerned

with epidemics of communicable diseases.

Then epidemiology was extended to

endemic communicable diseases and non-

communicable infectious diseases.

04/19/2023 12

More recently, epidemiologic methods

have been applied to chronic diseases,

injuries, birth defects, maternal-child

health, occupational health, and

environmental health

04/19/2023 13

Now, even behaviours related to health

and well-being (amount of exercise, seat-

belt use, etc.) are recognized as valid

subjects for applying epidemiologic

methods.

“disease”. Refer to the range of health-

related states or events.

04/19/2023 14

Specified populations. Although epidemiologists

and physicians in clinical practice are both

concerned with disease and the control of disease,

they differ greatly in how they view “the patient.”

Clinicians are concerned with the health of an

individual; epidemiologists are concerned with

the collective health of the people in a

community or other area.

04/19/2023 15

When faced with a patient with diarrheal

disease, for example, the clinician and the

epidemiologist have different responsibilities.

Although both are interested in establishing

the correct diagnosis, the clinician usually

focuses on treating and caring for the

individual.

04/19/2023 16

The epidemiologist focuses on the exposure

(action or source that caused the illness), the

number of other persons who may have been

similarly exposed, the potential for further

spread in the community, and interventions to

prevent additional cases or recurrences.

04/19/2023 17

Application. Epidemiology is more than “the study

of.” As a discipline within public health,

epidemiology provides data for directing public

health action. However, using epidemiologic data is

an art as well as a science. Consider again the

medical model used above: To treat a patient, a

clinician must call upon experience and creativity

as well as scientific knowledge.

04/19/2023 18

Similarly, an epidemiologist uses the

scientific methods of descriptive and

analytic epidemiology in “diagnosing”

the health of a community, but also must

call upon experience and creativity

when planning how to control and

prevent disease in the community.

04/19/2023 19

Other definitions of terms Data-Raw facts and figures Information-analyzed and interpreted

data Health information systems- organized

set of activities and programs whose purpose is to gather, maintain, and provide health related information to improve individual or population health

Vital statistics- combination of vital and health statistical data-mortality, morbidity, life expectancy, births, marriages, divorces, census

04/19/2023 20

Rates- amount or number of one thing measured in units of another

- Measure of an event/condition with a unit of population and within a time period

- No of cases/population of area in time x 1,000 Crude rates- Number of events that happen in

population in certain period of time Define the following terms: Infant mortality rates Neonatal mortality rates Postneonatal mortality rates Maternal mortality rates Perinatal mortality rates

04/19/2023 21

Data sourcesRegistration systems

Vital-event registrationDisease notificationsSentinel notifications

StudiesSurveysRegistriesEpidemic investigationsPopulation & house censusresearch

04/19/2023 22

OtherAdministrativeProgram evaluationPublic health surveillanceExit interviews & FGDOther data banks

04/19/2023 23

Uses of Epidemiology Monitoring the health of a community,

region, or nation Surveillance, accident reports Identifying risks in terms of probability

statements Studying trends over time to make

predictions for the future Smoking and lung cancer Estimating health services needs

04/19/2023 24

04/19/2023 25

The Epidemiologic Triad:Agent, Host, and EnvironmentThe epidemiologic triangle or triad is the traditional model of infectious disease causation. It has three components: an external agent, a susceptible host, and an environment that brings the host and agent together. In this model, the environment influences the agent, the host, and the route of transmission of the agent from a source to the host.

04/19/2023 26

Epidemiologic triangle and triad

Host

Agent Environment

04/19/2023 27

Agent factors Agent originally referred to an infectious micro-organism

—virus, bacterium, parasite, or other microbe. Agents must be present for a disease to occur i.e they

are necessary but not always sufficient to cause disease.

As epidemiology has been applied to non-infectious conditions, the concept of agent in this model has been broadened to include chemical and physical causes of disease. These include chemical contaminants, such as the l-tryptophan contaminant responsible for eosinophilia myalgia syndrome, and physical forces, such as repetitive mechanical forces associated with carpal tunnel syndrome. NB: it is not always clear whether a particular factor should be classified as an agent or as an environmental factor.

 

04/19/2023 28

Host factors

Host factors are intrinsic factors that influence an individual’s

exposure, susceptibility, or response to a causative agent.

Age, race, sex, socioeconomic status, and behaviours

(smoking, drug abuse, lifestyle, sexual practices and

contraception, eating habits) are just some of the many host

factors which affect a person’s likelihood of exposure.

Age, genetic composition, nutritional and immunologic

status, anatomic structure, presence of disease or medications,

and psychological makeup are some of the host factors which

affect a person’s susceptibility and response to an agent.

04/19/2023 29

Environmental factorsEnvironmental factors are extrinsic factors which affect the agent and the opportunity for exposure.

Generally, environmental factors include physical factors such as geology, climate, and physical surroundings (e.g., a nursing home, hospital); biologic factors such as insects that transmit the agent; and socioeconomic factors such as crowding, sanitation, and the availability of health services.

Agent, host, and environmental factors interrelate in a variety of complex ways to produce disease in humans. Their balance and interactions are different for different diseases.

04/19/2023 30

END

MEASURES OF ASSOCIATION/IMPACT/OUTCOME MEASURES LESSON 2

04/19/2023By Nesidai 31

MEASURING EPIDEMIOLOGICAL OUTCOMES

04/19/2023By Nesidai 32

A proportion with the specification of time(e.g. deaths in 2000 / population in 2000)

Rate

A ratio where the numerator is included in the denominator (e.g. males / total births)

Proportion

Relationship between any two numbers(e.g. males / females or x/y) The numerator is not included in the denominator

Ratio

OUTCOME MEASURES Compare the incidence of disease among people

who have some characteristic with those who do

not

The ratio of the incidence rate in one group to that

in another is called a rate ratio or relative risk (RR)

The difference in incidence rates between the

groups is called a risk difference or attributable

risk (AR)

04/19/2023By Nesidai 33

CALCULATING OUTCOME MEASURES

04/19/2023 By Nesidai 34

Outcome

D

B

No Disease(controls)

IN = C / (C+D)CNot Exposed

IE = A / (A+B)AExposed

Incidence

Disease(cases)

Exposure

Relative Risk = IE / IN

Attributable Risk = IE - IN

04/19/2023 By Nesidai 35

1,1001,000100

730

370

Total

Lung Cancer

700

300

No

30/730 = 41 per 100030Non-smoker

70/370 = 189 per 100070Smoker

IncidenceYesExposure

Relative Risk = IE / IN = 189 / 41 = 4.61

Attributable Risk = IE - IN = 189 - 41 = 148 per 1000

Smokers are 4.61 times more likely than nonsmokers to develop lung cancer

148 per 1000 smokers developed lung cancer because they smoked

04/19/2023By Nesidai 36

Relative Risk = IE / IN = 189 / 41 = 4.61

Attributable Risk = IE - IN = 189 - 41 = 148 per 1000

RR < 1 RR = 1 RR > 1

Risk comparison between exposed and unexposed

Risk for disease is lower in the

exposed than in the unexposed

Risk of disease are equal for exposed and unexposed

Risk for disease is higher in the exposed than in the unexposed

Exposure as a risk factor for the disease?

Exposure reduces disease

risk(Protective

factor)

Particular exposure is not a

risk factor

Exposure increases

disease risk(Risk factor)

04/19/2023 By Nesidai 37

ANNUAL DEATH RATES FOR LUNG CANCER AND CORONARY HEART DISEASE (CHD) BY SMOKING STATUS, MALES

04/19/2023By Nesidai 38

1000 – 500 = 500 per 100,000

127.2 – 12.8 = 114.4 per 100,000

AR

1000 / 500 = 2127.2 / 12.8 = 9.9RR

50012.8Non-smoker

1,000127.2Smoker

Coronary Heart DiseaseLung CancerExposure

Annual Death Rate / 100,000

SUMMARY

The risk associated with smoking is lower for CHD (RR=2) than for lung cancer (RR=9.9)

Attributable risk for CHD (AR=500) is much higher than for lung cancer (AR=114.4)

In conclusion: CHD is much more common (higher incidence) in the population, thus the actual number of lives saved (or death averted) would be greater for CHD than for lung cancer

04/19/2023By Nesidai 39

ODDS RATIO

a b a+b

c d c+d

a+c b+d a+b+c+d

Exposure

Odds of exposure having disease

Disease Odds of disease having exposure

ODDS RATIO

-The ODDS of getting disease in exposed = a

b- The ODDS of getting disease in unexposed = c

dODDS RATIO = (a/b)/(c/d) = axd cxb

(Cross-products Ratio)

FACTORS CONTRIBUTING TO THE EMERGENCE AND RE-EMERGENCE

OF INFECTIOUS DISEASES

Microbial adaption; e.g. Natural

genetic variations, recombinations

and adaptations e.g Influenza A

Changing human susceptibility;

e.g. mass immunocompromisation

with HIV/AIDS

Climate and weather; e.g.

diseases with Zoonotic vectors

such as West line Disease

(transmitted by mosquitoes) are

moving further from the tropics as

the climate warms

Economic development; e.g. use of

antibiotics to increase meat yield of

farmed cows leads to antibiotic

resistance

Breakdown of public health

Poverty and social inequality; e.g. TB

is primarily a problem in low-income

areas

Change in human demographics and

trade; e.g. rapid travel enabled SARS to

rapidly propagate around the globe

War and farmine

Bioterorism; e.g. 2001 Anthrax attacks

Dam and irrigation system

construction; e.g. malaria and other

mosquito borne diseases

Increasing trade in exotic animals for pets

and as food sources. eg, recent U.S.

outbreak of monkeypox, and use of exotic

civet cats for meat in China was found to

be the route by which the SARS

coronavirus made the transition from

animal to human hosts.

Increased and imprudent use of drugs

and pesticides has led to the devpt of

resistant pathogens, allowing many

diseases that were formerly treatable

to make a comeback (e.g. TB, malaria,

nosocomial, and food-borne infections)

Decreased compliance with

vaccination policy has also led

to re-emergence of diseases e.g.

measles and pertussis

Moreover, many important infectious

diseases have never been adequately

controlled on either the national or

international level. Infectious diseases

that have posed ongoing health

problems in developing countries are re-

emerging in the United States (e.g.,

food- and waterborne infections, dengue,

West Nile virus).

MEASURES OF DISEASE OCCURRENCE

NESIDAI LECTURE 3

These mainly refer to morbidity and mortality measures.

MORBIDITY:

- Describes frequency of illness within populations.

- Commonly used measures:

Incidence and Prevalence rates.

Note the most important tool for measures of disease is

the RATE. The RATIO and PROPORTION are also often

used.

RATIO:

Is the Relationship between any two numbers

(e.g. males / females) It’s the Simplest of the expressions.

Expresses a relationship in form of X : Y or X/Y

e.g. M:F. Males and Females are exclusive. What is in M is not included in F. (M/F)

PROPORTION:

Its a ratio where the numerator is included in the denominator (e.g. males / total births)

Usually expressed as % e.g. Proportion of all births that are male= Male births

Male + Female births

RATE:A proportion with the specification of time(e.g. deaths in 2000 / population in 2000)Rate important for disease measurement

because it gives probability or risk of disease in a defined population in a specified period of time.

Rate:= No of events in given time in a given

population X k Pop. at risk of event in same time in same pop.

INCIDENCE: Incidence is the rate of new cases of a disease or

condition in a population at risk during a time period

Deals with new cases of disease or event during specified period of time.

It measures probability that healthy people will develop disease in specified time period.

Population is disease free at the beginning of observation period.

Incidence is a rate Calculated for a given time period (time interval) Reflects risk of disease or condition

INCIDENCE DEFINITION: Incidence (per 1000)

= No. of new cases in given time period X kPop. at risk of disease in same time

Choice of 1,000 (k) in the rate is arbitraryIncidence is a rateCalculated for a given time period (time interval)Reflects risk of disease or condition

Numerator = only events or disease cases developed within specified time period.

Denominator = All at risk in specified time.

Those included must have potential of developing disease e.g. Cancer Cervix

INCIDENCE DEFINITION CONT…: However, most diseases have low

frequency and in most cases we deal with large pop. Difference in excluding/including the immunized is of little statistical significance.

If precision is required or condition is common, then denominator includes only those at risk e.g. measles vaccine trials. At risk, those who have not had measles.

TYPES OF INCIDENCE. Attack Rate is another type of incidence (So

is 20 attack rate.) Attack Rate is incidence of disease when pop.

at risk is exposed for short time e.g. Epidemics (Food poisoning).

20 Attack Rate - Measures No. of cases of disease developing during stated time among those in a closed group who are susceptible.

It measures infectivity of disease.= No of new cases in grp minus No of

initial casesNo of susceptible in grp minus initial cases

CUMULATIVE INCIDENCE AND INCIDENCE DENSITY Sometimes period time over which persons

are observed may vary due to deaths, varying joining time in study.

Person - time denominators are then used. Here each case contributes unequal time to

study. All must be included. The person time unit is thus created.

There are 2 types of incidence measures:- Cumulative Incidence (CI)- Incidence Density (ID).

CUMULATIVE INCIDENCE AND INCIDENCE DENSITY

Cumulative Incidence: = No of new cases of disease in given period of

time X 1,000 Total pop. At risk during same time

It estimates probability or risk that one will be sick in given period of time.

Incidence Density:= No of new cases in given period of time

Total person - time of observation

INCIDENCE DENSITY

Person-time is valid when:- Risk of death or disease is constant through out study.- Disease or death rates are the same all

through i.e. for those still in study and those lost to follow up.

SUMMARY INCIDENCE : It measures rapidity with which disease develops in pop.

It is a more useful measure of risk cause it has measure of time. It is thus a true rate.

It is direct indicator of risk of disease. It indicates pop. free of disease at stat. of

observation time developing disease during observation.

INCIDENCE CONT…: Incidence is used in aetiologic studies of both chronic and

acute forms (e.g. Snow & cholera)

Increasing incidence rates provide clues on disease aetiology especially if one can determine the exposures that occured before onset of disease.

Decreasing incidence rates may be due to results of disease control or prevention programme, or may be due to changes in host or agent characteristics (resistance / immunity).

Increasing incidence rates might suggest:- Need for new control or prevention programme.- That reporting practices improved.- That diagnostic procedure are more sensitive- Or ALL.

INCIDENCE CONT…:

To determine incidence, must be able to classify subjects into diseased or not diseased.

Screening method is therefore necessary

PREVALENCE:Prevalence is the proportion of the population

affectedAbout existing disease cases in pop. at point in

time or specified period of time.Prevalence is a proportion Point Prevalence: at a particular instant in timePeriod Prevalence: during a particular interval of

time (existing cases + new cases)Measures those already with disease i.e. gives the

probability that person has disease at a given time.Cases included are both old and new.Prevalence depends on:

- Rate of Cure- Recovery- Death

Prevalence is a proportion

Point Prevalence: at a particular instant in time

Period Prevalence: during a particular interval of time (existing cases + new cases)

Prevalence= Number of existing cases

Total number in the population at risk

PREVALENCE CONT…:

Prevalence thus reflects the incidence and duration of disease.

In a stable pop. : - Prevalence = Incidence X Average duration of disease

Prevalence describes amount of disease in pop. at point in time or period interval in time.

It does not measure rate of development of disease.

It is more correctly a ratio or proportion.

INCIDENCE AND PREVALENCE :

Incidence adds cases to prevalence: When incidence increrases, shows Risk. When prev. decreases, it shows cure or death. Prevalence may increases when cases not

dying but disease controlled e.g. insulin and diabetes.

When prevalence is increasing, difficult to convince that programme is working.

Disease may be controlled, but cure not achieved.

Health resource requirements & planning is determined by this.

PREVALENCE CONT… If type of prevalence is not mentioned, then regard it as

point prevalence.

In prevalence, onset of disease does not need to be known while in incidence it is necessary.Period prevalence is preferred than point prevalence or incidence because of establishing date on which disease started e.g. mental illnesses.

Prevalence is useful in:- Chronic diseases- Expressing burden of disease in pop.- Monitoring Control Programmes cause it reflects on duration and Incidence.- High prevalence does not necessary signify raised risk. It may mean longer survival of cases.

INCIDENCE AND PREVALENCE ILLUSTRATION:

1995 - Incidence= b + d

Point prevalence = (depends on which month count is made.- January = a + c + e- May = A + b + c + e- July - B + c + d + e- September = b + d + e- December = d + e

Period prevalence (1995) = a + b + c + d + e

PROBLEMS WITH INCIDENCE AND PREVALENCE MEASURES:

Defining who has disease (Numerator) Prevalence can be affected by diagnostic criteria used. Finding cases for inclusion:

- By interview- By data collected regularly (E.g. Hospital - Problems)

Hospital admissions selective on:- Personal characteristics- Severity of disease- Admission policies.

Comparability of cases (e.g. primigravidae in KNH, others).

Hospital rates have no denominator, i.e no catchment pop.

Denominator must be described well. In ca. Cervix denominator must exclude

RATES: CRUDE SPECIFIC ADJUSTED

CRUDE RATES:These don’t take into consideration certain crucial factors that impact on the rate. E.g. Age, sex, place.

Specific Rates:These take into consideration these factors.

ADJUSTED RATES:

Undergo statistical transformation to permit fair comparison between grps which differ in some characteristic that may affect risk of disease.

Transformation is carried out on crude rates to remove the effect of differences in composition of the various pops.

ADJUSTED RATES:

Adjustment is done cause pop. compositions in two different periods may differ.

One may have older people which affects mortality.

Adjustment removes the influence of age on rates being compared.

Exercises Handout

TABLE 1:COMPARABILITY OF 2 POPULATIONS WITH SAME AGE STRATA

Population as of July, Population as of July,1st, 1940 1st, 1980

Age grp(Yrs). (1) (2) _______________________________________________________________________

< 5 10,541 16, 348,0005-9 10,685 16, 700,00010 – 14 11,746 18, 242,00015 – 19 12,334 21, 168,00020 – 24 11,588 21, 319,00025 – 29 11,097 19, 521,00030 – 34 10,242 17, 561,00035 – 39 9,545 13, 965,00040 – 44 8,788 11, 669,00045 – 49 8,255 11, 090,00050 – 54 7,257 11, 710,00055 – 59 5,844 11, 615,00060 – 64 4,728 10, 088,00065 – 74 6,377 15, 581,00075+ 2,643 9, 969,000

Total 131,670 226,546,000

TABLE 2:COMPARISON OF 2 POPULATIONS FOR SPECIFIC AND CRUDE CANCER MORTALITY RATES:

Cancer Mortality Rates per 100,000_________________________________________

(Yrs). (1940) (1980) _______________________________________________________________________

< 5 4.7 4.25-9 3.0 4.710 – 14 2.9 3.915 – 19 4.0 5.420 – 24 6.8 7.225 – 29 11.6 10.530 – 34 23.5 17.335 – 39 43.4 33.540 – 44 80.3 66.945 – 49 133.4 128.350 – 54 209.0 228.955 – 59 309.9 358.260 – 64 443.3 25.865 – 74 695.1 817.975+ 1183.5 1313.7

Total 120.2 183.8

ADJUSTED RATES E.g. Crude mortality rate from cancer in USA in 1940 was 120.2

per 100,000 and in 1980, rate was 183.8 per 100,000.

When compare the 2 rates it suggests that, the rate is increased alarmingly by 53% (This is an epidemic).

(183.8 – 120.2 = 63.2 X 100 ) 120.2

Problem of comparing the 2 directly is that;In 1980, 11% of the population was 65 years or older while in 1940, this proportion was 6.9%. (i.e. the population in 1980 is older

Mortality rates from most cancers increase dramatically with age.

The higher crude cancer mortality rates are attributed in part, at least, to ageing of the population.

ADJUSTED RATES CONT….:

Thus any crude rate is a- Weighted average of individual age category

specific rates- Weight here is the proportion in the pop. that each

age category contributes to total rate.- Thus if < 5 yrs are 1,000,000 then more deaths will

be recorded than if the total pop. is 100,000.- Thus if 2 pops have the same stratum specific rates,

the 2 will differ in crude rates if proportion (number) of pops within each of the various categories are different.

ADJUSTED RATES CONT…:

2 ways of accounting for different distributions of a characteristic between populations being compared is

- Either present and compare only the category specific ratese.g. 1940 – 1980, though crude rates increased by 53% most age specific rates increased only slightly,

- In fact for < 5 years and those between 25 and 49 years, mortality rates actually decreased

Comparing specific rates is thus more accurate than the crude rates.

ADJUSTED RATES CONT…:

However one requires large numbers, each age group has to be scrutinized and compared with another.

It becomes easier to have a summary rate to compare with another.

Summary takes into account any differences in the structure of a population.

The procedure used to do this is called Adjustment or Standardization.

ADJUSTED RATES CONT..:

Adjusted rates are also standardized rates. Age is variable for which most adjustment or

standardization is required.2 ways of removing effect of differences in pop is (Standardization):- Direct method - Indirect method

DIRECT METHOD CONT..: Select standard Pop. The standard pop. is arbitrarily selected. Identify two grps being compared. Then apply age specific mortality rates of each

grp to the pop. in same age grp of the standard pop.

This gives number of deaths that can be expected if these age specific rates prevailed on the standard pop.

TABLE 3

CALCULATION OF CRUDE AND AGE SPECIFIC MORTALITY RATES FROM CANCER (1980)

Age Number of Population as Mortality rate perGroup (Years) Cancer Deaths of July 1, 1980 100,000 (1) (2) (3)____________________________________________________________________< 5 686 16,348,000 5 - 9 777 16,700,000 10 - 14 720 18,242,000 15 - 19 1145 21,168,000 20 - 24 1538 21,319,000 25 - 29 2041 19,521,000 30 - 34 3040 17,561,000 35 - 39 4684 13,965,000 40 - 44 7786 11,669,00045 - 49 14,230 11,090,00050 - 54 26,800 11,710,000 55 - 59 41,600 11,615,000 60 - 64 53,045 10,088,00065 - 74 127,430 15,581,00075 + 130,959 9,969,000Total 416,481 226,546,000

(3) = (1) / (2)

TABLE 4CALCULATION OF THE CRUDE CANCER MORTALITY RATE AS A WEIGHTED AVERAGE OF AGE SPECIFIC RATES (1980)

Age Mortality rate per Population as Number ofGroup 100,000 of July 1, 1980 Cancer Deaths(Years) (1) (2) _____________________________________________________________________________< 5 4.2 (a) 16,348,000 (i) 5 - 9 4.7 (b) 16,700,000 (ii) 10 - 14 3.9 (c) 18,242,000 (iii) 15 - 19 5.4 (d) 21,168,000 (iv) 20 - 24 7.2 (e) 21,319,000 (v) 25 - 29 10.5 (f) 19,521,000 (vi) 30 - 34 17.3 (g) 17,561,000 (vii) 35 - 39 33.5 (h) 13,965,000 (viii) 40 - 44 66.7 (i) 11,669,000 (ix)45 - 49 128.3 (j) 11,090,000 (x)50 - 54 228.9 (k) 11,710,000 (xi) 55 - 59 358.2 (l) 11,615,000 (xii) 60 - 64 525.8 (m) 10,088,000 (xiii)65 - 74 817.9 (n) 15,581,000 (xiv)75 + 1313.7 (p) 9,969,000 (xv)Total 226,546,000 (Z)

Crude 1980 cancer death rate = (1a) X (2i) + (1b) X (2ii) + (1c) X (2iii) .......... per 105

Z

= 183.8/105

TABLE 5CALCULATION OF THE CRUDE CANCER MORTALITY RATE AS A WEIGHTED AVERAGE OF AGE SPECIFIC RATES, WITH A DIFFERENT AGE DISTRIBUTION OF THE POPULATION. (1980)

Age Mortality rate per Population as Number ofGroup 100,000 of July 1, 1980 Cancer Deaths(Years) (1) (2) _____________________________________________________________________________< 5 4.2 (a) 16,348,000 (i) 5 - 9 4.7 (b) 16,700,000 (ii) 10 - 14 3.9 (c) 18,242,000 (iii) 15 - 19 5.4 (d) 21,168,000 (iv) 20 - 24 7.2 (e) 9,969,000 (v) 25 - 29 10.5 (f) 19,521,000 (vi) 30 - 34 17.3 (g) 17,561,000 (vii) 35 - 39 33.5 (h) 13,965,000 (viii) 40 - 44 66.7 (i) 11,669,000 (ix)45 - 49 128.3 (j) 11,090,000 (x)50 - 54 228.9 (k) 11,710,000 (xi) 55 - 59 358.2 (l) 11,615,000 (xii) 60 - 64 525.8 (m) 10,088,000 (xiii)65 - 74 817.9 (n) 15,581,000 (xiv)75 + 1313.7 (p) 21,319,000 (xv)Total 226,546,000(Z)

Crude 1980 cancer death rate = (1a) X (2i) + (1b) X (2ii) + (1c) X (2iii) .......... per 105

Z

= 249.2/105

TABLE 6.CALCULATION OF THE CRUDE CANCER MORTALITY RATE AS A WEIGHTED AVERAGE OF AGE SPECIFIC RATES (1980)

Age Mortality rate per Population Group 100,000 (1940) 1940 (in thousands)(Years) (1) (2) _____________________________________________________________________________< 5 4.7 (a) 10,541 (i) 5 - 9 3.0 (b) 10,685 (ii)10 - 14 2.9 (c) 11,746 (iii) 15 - 19 4.0 (d) 12,334 (iv) 20 - 24 6.8 (e) 11,588 (v)25 - 29 11.6 (f) 11,097(vi) 30 - 34 23.5 (g) 10,242 (vii) 35 - 39 43.4 (h) 9,545 (viii)40 - 44 80.3 (i) 8,788 (ix)45 - 49 133.4 (j) 8,255 (x)50 - 54 209.0 (k) 7,257 (xi)55 - 59 309.9 (l) 5,844 (xii)60 - 64 443.3 (m) 4,728 (xiii)65 - 74 695.1 (n) 6,377(xiv)75 + 1183.5 (p) 2,643(xv)Total 120.2 131,670

Crude 1940 cancer death rate = (1a) X (2i) + (1b) X (2ii) + (1c) X (2iii) .......... per 105

Z

= 120.2/105

TABLE 7CALCULATION OF THE AGE -ADJUSTED MORTALITY RATES FROM ALL CAUSES BY THE DIRECT METHOD.

Standard Population: Expected Number

Mortality from all Total US Enumerated Of Deaths that Would

Causes per 100,000 population Occur in Standar

Population Population Rates in

_________________ ___________________ _________________

Age 1950 1960 1940 1950 1960

Group

(Years) (1) (2) (3) (4) (5)

_____________________________________________________________________________

< 1 3,299.2 2,696.4 15,343 506.2 413.7

1- 4 139.4 109.1 64,718 90.2 70.6

5 - 14 60.1 46.6 170,355 102.4 79.4

15 - 24 128.1 106.3 181,677 232.7 193.1

25 - 34 178.7 146.4 162,066 289.6 237.6

35 - 44 358.7 299.4 139,237 499.4 416.9

45 - 54 853.9 756.0 117,811 1,006.0 890.7

55 - 64 1,901.0 1,735.1 80,294 1,526.4 1,393.2

65 – 74 4,104.3 3,822.1 48,426 1,987.5 1,850.9

75 - 84 9,331.1 8,745.2 17,303 1,614.6 1,513.2

85+ 20,196.9 19,857.5 2,770 559.5 550.4

Total death

rate all ages 963.8 954.7 ___ ___ ___

Total Pop. ___ 1,000,000 ___ ___

Total Expected

Number of Deaths ____ ____ 8,414.5 7,609.7

Age Adjusted Death

Rate per 100,000 ____ ____ 841.45 760.97

_____________________________________________________________________________

(4) = (1) X (3)

(5) = (2) X (3)

INDIRECT METHOD: (STANDARDIZED MORT. RATIO)

Select a standard Pop. whose age specific death rates are known.

Use this to calculate expected death rates in pop. being compared.

Calculate S.M.R.= Observed deaths X 100

Expected deaths

INDIRECT METHOD CONT…:

Here compare 2 pops.- One in which age specific death rates aren’t known or if known are excessively variable because of small numbers involved.- Most stable rates of larger pop. are applied to pop of smaller one.

Then calculate standardized mortality Ratio.

TABLE 6CALCULATION OF THE STANDARDIZED MORTALITY RATIO FOR OCCUPATION OF MALE FARMERS AND FARM MANAGERS FOR ALL CAUSES OF DEATH .

Standard Death Rates Expected Number

Number of Farmers Per 1,000,000 (all Of Deaths for farmers

And Farm Managers causes of Death) and farm managers

(Census 1951) Per 1,000,000

Age

Group

(Years) (1) (2) (3) = (1) X (2)

_____________________________________________________________________________

20 - 24 7,989 1,383 11

25 - 34 37,030 1,594 59

35 - 44 60,838 2,868 174

45 - 54 68,687 8,212 564

55 - 64 55,565 22,953 1,275

_____________________________________________________________________________

Total Expected Deaths per Year: 2,083 (E)

Total Observed Deaths per Year: 1,464 (O)

SMR = 1,464 X 100 = 70.3%

2,083

INDIRECT METHOD CONT…:

S.M.R.Column 1X column 2 = Column 3

= 2,083 ExpectedTotal observed is given 1,464

= Observed - 1,464 X 100 = 70.3%Expected - 2,083

PROPORTION V/S INCIDENCE

Proportion of all those with Cancer incidence in each age group

0

50

100

150

200

250

300

20 25 30 35 40 45 50 55 60 65 70 75 80 85

Age (Yrs)

An

nu

al r

ate

pe

r 1

00

,00

0

0

2

4

6

8

10

12

14

16

18

% N

o o

f c

as

es

PROPORTIONS V/S INCIDENCE RATE CONT…:

Line is incidence. Shows risk of breast cancer throughout life.

It is computation of risk of cancer within age group.- At 45 yrs curve changes.- Shows higher probability of cancer here - This is pre and post menopause in women.- Pattern is the same in women in all countries.- Probably pre and post menopausal breast cancers are different diseases.

PROPORTIONS AND INCIDENCE RATE:

Bar graph is % of total population with breast cancer.

Trend is different in that it shows reduction with age.

REASONS:- Fewer older people exist and contribute a small proportion to total.- Hence only 5% of breast cancer cases occur in oldest age grp.- Gives impression that lesser attention

required at old age than the young