INTRODUCTION TO THE ROLE OF STATISTICS IN PUBLIC HEALTH AND CLINICAL MEDICINE HADYANA SUKANDAR

LESSON 1 : DEFINITIONS OF STATISTICS THE TERM “STATISTICS” IS USED IN TWO WAYS. FIRST, IT REFERS TO THE EVERYDAY USE OF : - DATA - NUMERICAL OBSERVATION - QUANTITATIVE INFORMATION

Examples : 1. Number of trained community health workers in the different districs of the country 2. Birth weights of babies 3. Age (in completed years) of patients seen an outpatient clinic on a specific day 4. Prevalence of DM in local government areas

STATISTICS ALSO REFERS TO THE DISCIPLINE, COMPRISING : - STATISTICAL METHODS - THE STUDY OF SCIENTIFIC METHODS OF COLLECTING, PROCESSING, REDUCING, PRESENTING, ANALYSING AND INTEPRETING DATA, AND OF MAKING INFERENCES AND DRAWING CONCLUSIONS FROM NUMERICAL DATA MAIN USES OF STATISTICAL METHODS THREE MAIN USES OF STATISTICAL METHODS ARE :

(A) TO COLLECT DATA IN THE BEST POSSIBLE WAYS THIS INCLUDES METHODS OF : - DESIGNING FORMS FOR DATA COLLECTION - ORGANIZING THE COLLECTION PROCEDURE - DESIGNING AND EXECUTING RESEARCH - CONDUCTING SURVEYS IN A POPULATION Examples : 1. Collection of data on participants in a disease intervention programme 2. Systematic collection of data on births and deaths 3. Collection of data on persons with pulmonary tuberculosis in a defined population

(B)TO DESCRIBE THE CHARACTERISTICS OF A GROUP OR A SITUATION THIS IS ACCOMPLISHED MAINLY BY : -DATA REDUCTION -DATA SUMMARY -DATA PRESENTATION (C)TO ANALYSE DATA AND TO DRAW CONCLUSIONS FROM SUCH ANALYSES THIS INVOLVES THE USE OF VARIOUS ANALYTICAL TECNIQUES AND THE USE OF PROBABILITY CONCEPTS IN DRAWING CONCLUSIONS

USE OF STATISTICAL CONCEPTS IN MEDICINE : (A)HANDLING OF VARIATION Variation in a characteristics (or factor, or measurement) occurs when its value changes from subject to subject, or from time to time within the same subject. EXAMPLES : AGE, WEIGHT, HEIGHT, BLOOD PRESSURE, CHOLESTEROL LEVEL, BILIRUBIN, ALBUMIN, IMMUNOGLOBULIN LEVELS, GLUCOSE LOAD.

(B)DIAGNOSIS OF PATIENS’ AILMENTS AND COMMUNITY HEALTH (C)PREDICTION OF LIKELY OUTCOME OF A DISEASE INTERVENTION PROGRAMME IN COMMUNITY OR OF DISEASE IN INDIVIDUAL PATIENTS (D)SELECTION OF APPROPRIATE INTERVENTION FOR A PATIENT OR COMMUNITY (E)PUBLIC HEALTH, HEALTH ADMINISTRATION, AND PLANNING

COLLECTION AND ORGANIZATION OF DATA AND SCALES OF MEASUREMENT 1.REGULAR AND AD HOC SYSTEMS FOR COLLECTING DATA A REGULAR OR ROUTINE SYSTEM OF DATA COLLECTION USUALLY CONSISTS OF A MECHANISM ( REGISTRATION PROCEDURE) FOR COLLECTING DATA AS THEY BECOME AVAILABLE. LESSON 2 :

EXAMPLES : 1.A VITAL STATISTICS REGISTRATION SYSTEM TO COLLECT DATA ON BIRTHS, DEATHS, MARRIAGES AND DIVORCES 2.A DISEASE NOTIFICATIONS SYSTEM TO COLLECT INFORMATION ON CHOLERA, YELLOW FEVER, ETC 3.A REPORTING SYSTEMS FOR CANCER CASES (CANCER REGISTRY) 4.REGISTRATION SYSTEMS IN HEALTH CARE FACILITIES, TO COLLECT INFORMATION ON PATIENTS ATTENDING THE VARIOUS CLINICS.

AD HOC COLLECTION OF DATA IS USUALLY IN THE FORM OF A SURVEY TO COLLECT INFORMATION THAT IS NOT AVAILABLE ON A REGULAR BASIS. THIS MAY INCLUDE SPECIAL INVESTIGATIVE STUDIES OR AN ELABORATION OF ASPECTS OF DATA THAT HAVE BEEN COLLECTED ON A REGULAR BASIS. EXAMPLES : 1.A NATIONAL HEALTH MANPOWER SURVEY 2.A SURVEY TO ESTIMATE THE PROPORTION OF CHILDREN WITH MALNUTRION IN A DEFINED POPULATION 3.AN INVESTIGATION OF BREAST-FEEDING PRACTICES AMONG WOMEN WHO REGISTERED A BIRTH IN THE PREVIOUS YEAR.

2.PROCEDURES FOR DATA COLLECTION (AD HOC SYSTEM) A. DEFINITION OF STATEMENT OF THE OBJECTIVES OF THE COLLECTION EXERCISE, INDICATING WHAT TYPE OF INFORMATION NEEDS TO BE COLLECTED, AND HOW IT IS TO BE USED B.DEFINITION OF POPULATION ON WHICH INFORMATION IS REQUIRED (THE REFERENCE OR TARGET POPULATION) C.DECISION ON WHETHER INFORMATION WILL BE COLLECTED FROM ALL UNITS IN THE REFERENCE POPULATION OR FROM A SELECTION OF THEM

D.DECISION ON HOW MANY RESPONDENTS ARE TO BE INCLUDED IN THE STUDY E.DECISION ON HOW THESE RESPONDENTS WILL BE SELECTED F.DESIGN OF THE INTRUMENTS (FORMS, ETC.) TO BE USED FOR RECORDING DATA G.SELECTION AND TRAINING OF PERSONNEL TO RECORD THE INFORMATION H.DATA COLLECTING : IDENTIFICATION OF SELECTED UNITS AND RESPONDENTS, FILLING OF FORMS, ETC.

3. INSTRUMENTS FOR MEASURING DATA A. APPARATUS : MEASUREMENT IS DONE PURELY MECHANICAL DEVICE. EXAMPLE : WEIGHING SCALES, THERMOMETERS B.HUMAN : MEASUREMENT IS DONE BY PERSONS. EXAMPLE : TAKING A PATIENT’S HISTORY C.COMBINATION OF APPARATUS AND HUMAN. EXAMPLES: READING OF X-RAY FILMS, READING OF BLOOD FILMS. 4.RELIABILITY AND VALIDITY PROCEDURES TWO DESIRABLE CHARACTERISTICS OF INSTRUMENTS FOR MEASURING DATA ARE RELIABILITY AND VALIDITY.

A MEASUREMENT VARIABLE DESCRIBE A CHARACTERISTIC IN TERMS OF A NUMERICAL VALUE, THE VALUE MAY VARY FROM SUBJECT TO SUBJECT OR FROM TIME TO TIME IN THE SAME SUBJECTS. EXAMPLES: HEIGHT IN M, WEIGHT IN KG. A DESCRIPTIVE ATTRIBUTE IS A CATEGORY OF A CHARACTERISTIC, TO WHICH A SUBJECT EITHER BELONGS OR DOES NOT BELONG, OR A PROPERTY OR QUALITY THAT A SUBJECT EITHER POSSESSES OR DOES POSSESS. EXAMPLES : ACCESS TO SOME FORM OF HEALTH CARE, SICKNESS, HOSPITALIZATION, TYPE A BLOOD. 5.VARIABLES AND ATTRIBUTES

A CONTINUOUS VARIABLE IS ONE WITH POTENTIALLY AN INFINITE NUMBER OF POSSIBLE VALUES IN ANY INTERVAL. IT CAN ASSUME EITHER INTEGRAL OR FRACTIONAL VALUES, AND CAN BE MEASURED TO DIFFERENT LEVELS OF ACCURACY BY USING MORE OR LESS REFINED METHODS OF MEASUREMENT. EXAMPLES: HEIGHT (IN METRES) : 1.83; 1.74 WEIGHT (IN KG) : 48.7;90. A DISCRETE VARIABLE CAN ONLY HAVE A FINITE NUMBER OF VALUES IN ANY GIVEN INTERVAL. THE VALUES ARE USUALLY WHOLE NUMBERS. EXAMPLES : NUMBER OF HOUSEHOLDS IN A COMMUNITY, WHITE BLOOD CELL COUNT, NUMBER OF BEDS IN HOSPITAL. 6. CONTINUOUS AND DISCRETE VARIABLES

- NOMINAL (SEX, BLOOD TYPE, ETC) - ORDINAL (SOCIAL STATUS, EDUCATION,ETC) - INTERVAL (BODY TEMPERATURE, SISTOLIC BLOOD PRESURE, ETC) - RATIO (HEIGHT, WEIGHT, ETC) 7.SCALES OF MEASUREMENT

CATEGORICAL DATA ARE MEASUREMENTS IN WHICH THE NOTION OF MAGNITUDE IS ABSENT OR IMPLICIT. SUCH VARIABLES ARE MEASURED EITHER ON A NOMINAL OR AN ORDINAL SCALE. QUANTITATIVE DATA HAVE MAGNITUDE. THEY ARE MEASURED EITHER ON AN INTERVAL OR ON A RATIO SCALE. 8.QUANTITATIVE AND CATEGORICAL DATA