Dr. Bassam HijawiEpidemiologist Director of Jordan Cancer RegistryDirector of Health Promotion
In Epidemiology The most important tool for measuring the risk of occurrence of a particular event in a population during a given time period are :-
Rates Morbiditly Rats: Measuring the occurrence (probability , risk) of disease (includes illness, injury, or disability). A term preferably avoided, used incidence rate or prevalence rate Mortality Rates: Measuring the occurrence of deaths. A term preferably a voided, many crude and specific death rates used. (indices of health ).
Rates , may be : Crude Rates. Specific Rates. Standardized (adjusted ) Rates. • Example : • Population : 6,000 Men • 4,000 Women • 10,000 Total • Proportion : tell us what fraction of the population is affected . • Proportion of men = • = 0.60 = 60% • - Ratio M/F = • Ratio F/M =
Example : • ( 40) new cancer lung cases reported during the yare 2004 from the previous population (30 among men and 10 among Women ). 6 cases died during the same year . (5 among men and 1 among women ) Rates : tell us how fast the disease is occurring in a population . • Lung Cancer Incidence Rate = • Female Lung cancer Incidence Rate = • Lung cancer death Rate =
Measures of Disease Occurrence Morbidity Rates Routinely collected data on illness from different sources : • Incidence Rate: The number of new cases of a disease that occur during a specified period of time in a population at risk for developing a disease . IR per 1000 No. of new cases of a disease occurring in the population during a specified of time = _________________________________________________________________ x 1000 No. of persons at risk of developing the disease during that period of time
The disease developed in a person who did not have the disease previously. • Transition from a non disease to diseased state. • Measure of risk in exposed population . • Denominator = number of people who are at risk for developing the disease (estimated mid year population ) • Any individual in the denominator, may (must have) to become counted in the numerator. (numerator included in the denominator). • Incidence for uterine cancer, the denominator must be women. Mean, men not at risk to develop uterine cancer. • Period of time must known, must specified for all individuals in the denominator. Incidence may be calculated in one week, one month, one year, 5 years.
Pupulation at risk in a study of cervix carcinoma Defining pop. At risk: • Improve accuracy ( rate not diluted . • People who cannot contract the dis. are not included in the denominator. • Ex. • Occupational injuries occur among working people . • Brucellosis occur among people handling infected animals . (farms + slaughter houses 0-25 Y. All MEN AllWOMEN 25- 69 Y. 25- 69 Y. 70 + Y. Total Population All Women (Age groups Population At risk
Cumulative Incidence : • Example : 482 women using oral contraceptive, followed for 3 years . • 27 of them developed Bacterurea. • C.I of Bacterurea among O.C users = • ( Assume all persons have been followed during the 3 years period ) • Incidence Density : • Due to loss of follow up (attrition ) for any reason, different individual in the denominator, may be observed for different length of time, person- years used in the denominator. • (Unequal Periods of observation ) • Valid under these conditions: • Risk of disease or death is constant . Throught the study period. • Rate of disease or death the same between those lost to follow up and those not. • Disease under study must be not rapidly fatal.
2 3 5 4 2.5 Example: 1000 persons followed , (some leave, some dropout some die, some migrate… )end by 800 Example : Total years at risk16.5 ID = 2 cases / 16.5 person years = 12.1 / 100 person – years observation ( Incidence Density )
Attack Rats • It is incidence rate. • Usually expressed as percentage • Used for particular population . • Observed for limited period of time. • Used mostly in outbreaks/ epidemics.
Secondary attack rate • Used in propagated spread . Number of new cases in group minus initial case (s). • = ______________________________________ x 100 Number of susceptible persons in group minus initial case (s) • During a specified time period . • Index case (s) excluded from both numerator and denominator .
Specification of Numerator(Number of persons + Number of conditions) • More than one event can occur to the same person within stated time period . • This incidence rate tells us the number of events (colds) to be expected among the group of people in that year . • Incidence rate = Number of colds • PAR In one year period . • = Number of people who developed a cold • PAR In one year period. • This incidence rate tells us about the probability that any person will develop a cold in one year.
Mortality Rates • Annual M.R. for all causes /1000 POP. • Annual M.R from all causes for children younger than 10 Y. / 1000 POP. • restriction on age • applied to Num. + Denominator specific Rate Age specific M.R Restriction on dis./ specific // Cause Cause Specific Death Rate (No. of deaths from lung cancer in one year ). Leading cause of death Restriction for ( specific age and specific Cause ) Ex. Annual M.R for leuk. For children < 10 Y.
Case Fatality Rate Difference CDR + CFR * Measure of the severity of the dis. * Measure any benefits of a new therapy Therapy improve = CFR • Proportionate Mort. Rate. Means:What proportion of deaths attributed to Dis. X. ?
Comparison of M.R, PMR, All causes H.D P.M.R = give us a quick look at the major causes of deaths, but can not tell us the risk of dying from a dis. We Need M R for that .
Years of Potential Life LostYPLL Cause specific M.R 10th YPLL 6th In younger age Injuries, accidents, cancer… HIV Younger Involves a greater loss of future productive years than were it to occur at an older age.
When M R is a good index of incidence ? Measure of dis. risk • Under 2 conditions : • CFR is • Duration of dis is short ( Survival ) rabies Cancer pancreas • Problems with Mortality Data • Death Certificate Problems • [ underlying cause of death ] • [ Immediate cause of death ] • ICD
Ex. Breast Cancer I.R. in Women by age • Distinction between • Distribution of dis. • Proportion of cases • I.R (risk of the dis.). Age
Prevalence Rate ( P) • How many people have arthritis ? • Household Survey ? • Interviews , physical ex. • (I) + (P) difference We don’t take into account the duration of the dis. متى حدث Numerator mix . : not Measuring risk. Point Prevalence : (p) at a point in time Period Prevalence .
Ex. Questions regarding asthma Do you currently have asthma. ? Point Prevalence . Have you had asthma during the last (n) years? Period Prevalence . Have you ever had asthma. ? عمرك اصبت بالأزمة Cumulative Incidence
Mortality : Routinely collected data on deaths from different sources. • Crude Death Rate: • Specific Rates : A . Cause specific death rate: It means : • Risk of deaths from dis. (X). In POP. • Leading cause of deaths
B. Age specific death rate : It means : • What proportion of death attributed to Dis. X. ? C. Proportionate mortality rate : D. Case Fatality Rate : / Ratio It means : • Severity of the Disease .
Factors influencing observe Prevalence Rate Increased • Longer duration of dis. • Prolongation of life of patients without cure . • In new cases ( incidence ) • In – migration of cases. • Out –migration of healthy people . • In – migration of susceptible people. • Improved diagnostic facilities ( better reporting ) Decreased by • Shorter duration of dis. • Case – fatality rate from dis. • In new cases ( incidence ) • In – migration of healthy people • Out – migration of cases • Improved cure rate of cases
Relation Between (I), (p)ex. Using chest x rays, 2000 persons are screened for T.B, 1000 ( upper income people) from x area, and 1000 (lower income people ) from Y area . Can we conclude that the risk of T.B, is high in X than Y area ?
Descriptive Epidemiology • Study the distribution of disease within a population by person, place, and time. • Identify non-random variations in the distribution of disease to enable an investigator to generate testable hypotheses regarding etiology. - Who is getting the disease? - Where are the rats of disease highest and lowest? - When does disease occur commonly or rarely?
Descriptive Epidemiology Describe patterns of disease: (or) distribution of dis. within a population by person place time. Person Who is getting the dis.? Age, sex, Ethnic status, Religion, Marital status, occupation, social class, Education, … others Place where are the rates of dis. Highest and lowest? Geographical distribution. Time when Does the dis. Occur commonly or rarely?
Descriptive EpidemiologyPerson place timeWho here whenPerson:.1 Age:Most important variable.Distribution by age group Or disease frequency Explained by: Susceptibility Immunity Exposure Chronic diseases
-Some dis. Occur exclusively in one particular age group.Ex. Ca.Prostate, chronic conditions by age.Ex.Aarthritis is, 10 times more common in 45 – 46 than < 45 years.Ex.Dental problems by age.Ex.Skin wrinkling by age skin elasticity
Age specific death Rate Jordan - 1996all causes Total 80 Death 60 Male Rate/ 40 1000 Female 20 0-1 1-4 5-9 10-14 15-19 20-24 25-29 30-34 35-39 40-49 50-54 55-59 60-64 65-69 70-76 75-79 age groups
DEATH RATE 50.0 40.0 Developed. 20.0 10.0 Rate/ 5.0 1000 1.0 Developing .05 <1 1-4 5-14 15-24 25-34 35-44 45-54 55 - 64 65-74 75+ Age groups (y.)
%of pop. With limitation of activity - chronic dis. 60 50 48 40 30 20 10 20 20 - 44 45 - 64 65+ Age Groups (y.)
2. Gender: • Death Rates higher for Males than Females. • Sex Linked inheritance. • Difference in hormonal balance. • Environmental … Occupation. … exposure. … habit patterns. • Hereditary
High Morbidity + Low mortality in F. May be due to: • F. seek medical care more freely and at early stage of dis. • Dis. Tend to have less lethal course in F.than M. • Expectation of life more in F. than M.
3. Ethnic group [Race] : • Whites ad non – whites. • Cancer Cervix in blacks. Breast in whites. Stomach in Japanese.
4. Social class: • Occupation • Education } Total • Area of residence } life • Income } style Reflect : Nutrition, crowding. Personal hygiene and Medical Care Utilization.
Relationship between economic status and health care[ USA children, 6 - 11 years of age, grouped according to family income ] primary + permanent teeth Number of teeth Decayed Filled <3000 3-4.9 5-6.9 7-9.9 10-14.9 > 15000 < 3000 3-4.9 5-6.9 7-9.9 10-14.9 > 15000 Family Income (us $ ) economic status + health care USA children 6 – 11 y.
5. Occupation: * Spend 1/3 time working in different conditions affect health. * Exposure to: physical conditions: heat, cold, change atmospheric pressure, noise / Minining / construction / Diving ِ/Agriculture /injury and trauma. chemical : heavy metals (lead, mercury) , CO , So2 .. Biological : endemic dis. Occupational stress/jop: (hypertension, peptic ulcer, diabetes).
Exposure to: • Silica Pul. Fibrosis • Asbestos mesothelioma, ca. Lung • Aniline dyes bladder cancer • chromate Lung cancer
6. Marital Status: for women (sexual exposure, pregnancy, childbearing, Lactation..) (Single, married, divorced) Cancer Cervix: > in married than single women. Cancer Breast: > in single than married women. Cancer Breast: > in early age at first pregnancy. (Protected by Lactation).
7.Family Variable: • Family Size. • Birth order. • Present of both parents, or parent. deprivation. • Maternal age. • Religion of parents. • Position of index person.
8. Others: Immunization. Habits. Personality traits: Type A: CHD. Type B: CHD. A B O System: - Type A risk of gastric cancer - Type O risk of duodenal ulcer - Sickle cell trait: risk of malaria. (plas. falciparum.)
PLACE Freq. of dis. can be related to place of occurrence in terms of areas set off either by naturalbarriers as: mountains, rivers, deserts, and political boundaries. Or of certain dis. Due to particular env., climate,…. Temp., humidity., rainfall, water supply … etc.
- E.g. Tropical diseases.- Endemic diseases.- Certain fungal dis.- Endemic goiter in (iodine def. areas).- Mottled dental enamel … fluoride content of drinking water.- Melanoma of skin … sunlight.- Burkitts lymphoma … endemic in equatorial Africa. (Epstein – Barr Virus.)