FREQUENCY

IN

EPIDEMIO

LOGY

F AJ A

R A

WA

L I A Y

UL I A

NT

O

LAST SESSION

DOES ANYBODY STILL REMEMBER THE DEFINITION OF EPIDEMIOLOGY?

DISTRIBUTION

DETERMINANT

POPULATION

DISTRIBUTION

MEASURE THE FREQUENCY IN A DISEASE

THE PARAMETER OF THE FREQUENCY ARE:

1. COUNTS

2. RATIO1.PROPORTION2.RATE

COUNTS

THE SIMPLEST MEASURE IN EPIDEMIOLOGY

REFERS TO THE NUMBERS OF CASES OF A DISEASE OR OTHER HEALTH PHENOMENON BEING STUIDIED

e. g. NUMBER OF PERSONS WHICH BEEN NEWLY DIAGNOSED HAVING TUBERCULOSIS IS 245 THIS MONTH

USEFUL FOR ALLOCATION OF HEALTH RESOURCES

LIMITED USEFULLNESS FOR EPIDEMIOLOGIC PURPOSES WITHOUT KNOWING SIZE OF THE SOURCE POPULATION

RATIO

THE QUOTIENT OF 2 NUMBERS (NUMERATOR AND DENOMINATOR)

A QUANTITY DIVIDE THE QUANTITY

NUMERATOR MIGHT BE DIFFERENCE FROM THE DENOMINATOR (NUMERATOR MIGHT NOT INCLUDED IN DENOMINATOR)

e. g.

SEX RATIO= PROPORTION OF MALES/PROPORTION OF FEMALES

ACREDITATION=STUDENT/TEACHER

PROPORTION

TYPE OF RATIO, WITH THE NUMERATOR AS PART OF DENOMINATOR (NECESSARY!)

USUALLY MULTIPLIED BY 100, KNOWN AS PERCENTAGE

PROPORTION ALWAYS RANGES BETWEEN 0 AND 1

e. g. 16 CASES OF DISEASE FROM 48 PEOPLE. THE PROPORTION OF THE CASE IS 30%

RATE

TYPE OF RATIO THAT QUANTIFIES DYNAMIC PROCESS I. E. GROWTH AND ACCELERATION

FREQUENCY OF AN EVENT

RATE CONTAIN:• DISEASE FREQUENCY• UNIT SIZE IN POPULATION• TIME PERIOD DURING WHICH AN EVENT OCCURS

RATE = (NUMERATOR/DENOMINATOR)X F

NUMERATOR: SUM OF INDIVIDUAL EXPERIENCED IN AN EVENT

DENOMINATOR: SUM OF POPULATION AT RISK

F: CONSTANTA

REMEMBER

IN EPIDEMIOLOGY, WE HAVE TO DEFINE THE:

DISEASEPOPULATIONTIMEFRAME

DISEASE

ABNORMAL AMONG THE NORMALS

DIAGNOSED FROM:

1. SYMPTOMS

2. SIGNS

3. MEDICAL HISTORY

4. TEST RESULT

POPULATION

GROUP OF PEOPLE WITH THE SAME PURPOSES, LIMITED BY TIME AND PLACE

POPULATION AT RISK IS THE MAIN DENOMINATOR FOR DISEASE FREQUENCY IN EPIDEMIOLOGY (NOT THE POPULATION!)

CLASSIFICATION:

1. CLOSED POPULATION: SUBJECT ENTER AT THE SAME TIME AND THERE ARE VERY FEW LOSSES TO FOLLOW UP

2. OPEN POPULATION: SUBJECTS ENTER AT ANY TIME AND THERE ARE MANY LOSSES TO FOLLOW UP

TIMEFRAME

1. POINT (SNAPSHOT)

2. PERIOD (FOLLOWED)

BASIC MEASURE OF DISEASE FREQUENCY1. POINT PREVALENCE

2. PERIOD PREVALENCE

3. INCIDENCE PROPORTION

4. INCIDENCE RATE

PREVALENCE

POINT PREVALENCE

PROPORTION OF THE POPULATION AT RISK WHO HAVE THE DISEASE AT A PARTICULAR MOMENT (SNAPSHOT)

PERIOD PREVALENCE

PROPORTION OF THE POPULATION AT RISK WHO HAVE THE DISEASE WITHIN A CERTAIN PERIOD (VIDEOCAMERA)

POPULATION AT RISK IN PERIOD PREVALENCE IS (PARstart+PARend)/2

INCIDENCE

INCIDENCE PROPORTION (CUMULATIVE INCIDENT)REFLECTS THE ABSOLUTE RISK FOR DISEASE WITHIN A GIVEN

POPULATION

IP= N NEW CASES/N DISEASE FREE AT THE START OF FOLLOW UP

PEOPLE WHO HAVE THE DISEASE IS NOT INCLUDED IN DENOMINATOR

INCIDENCE RATE (INCIDENSE DENSITY,HAZARD RATE, PERSON TIME RATE, DISEASE INTENSITYTHE INCIDENCE RATE MEASURES THE PACE AT WHICH NEW

CASE OCCUR IN A POPULATION

IR=N NEW CASES/SUM OF DISEASE-FREE TIME OF EACH INDIVIDUAL

EACH PERSON OBSERVED UNTIL DIAGNOSIS OF DISEASE, END OF STUDY, LOSS TO FOLLOW UP

HOMEWORK ASSIGNMENT (FREQUENCY EPIDEMIOLOGY)PLEASE LOG IN TO:

http://vimeo.com/46161438 AND MAKE YOUR SUMMARY OF THER ANIMATION

TRUE OR FALSE. EXPLAIN THE ANSWER

1. WE CAN MEASURE THE INCIDENCE IN HOSTPITAL

2. PREVALENCE IS THE EXAMPLE OF RATIO

3. INCIDENCE IS THE EXAMPLE OF RATE

ALHAMDULILLAH