Fundamentals of Sampling Procedure

SAMPLING DR. SEEMA MUMTAZ 

SAMPLING PROCEDURE HAS TO FOLLOW THREE FUNDAMENTALS • IT IS REPRESENTATIVE • IS LARGE ENOUGH • THE SELECTED ELEMENTS HAVE BEEN PROPERLY  APPROACHED, INCLUDED & INTERVIEWED

SAMPLING SAMPLE IS A SUB SET OF

TOTAL POPULATION. IT HAS ALL INHERRANT QUALITIES OF POPULATION. WE CAN DERIVE INFERENCES ABOUT THE POPULATION POPULA TION FROM SAMPLE. SAMLE HAS TO BE A

REQUISITE FOR A RELIABLE REQUISITE SAMPLE : • EFFICIENCY  • REPRESENTATIVENESS • MEASURABILITY  • SIZE • COVERAGE • GOAL ORIENTED • FEASIBILITY  • ECONOMY & COST EFFICIENCY 

Ty   pe of sampling Type  procedures • Probability : each element has an equal chance of being included in the sample. 1. simple random. 2. Systematic. 3. Cluster. 4. Stratified.

• Non- probability :  There is no assurance that each element will have the same chance of being included in the sample. 1. Accidental. 2. Purposive. 3. Quota Sampling.

Probability  Probability Sampling Probability Sampling Simple Random: Simple Each unit has the same chance of being selected, only decide by the law of chance. Procedure: 1. Prepare a sampling frame-list show all the units. 2. Decide on the number to be selected-Samp Sample le size. It is some what difficult but very critical.  Three Three considerations in determination of sample size: ~ variability in the population. ~ amount of accuracy desired. ~ resource available to the researcher. ( table for determine sample size are available ). ~ type of study design. 3. Selected require numbers of units, through. ~ drawing lots ( lottery method ) comes out of lotto, a game of chance.

Probability  Probability Sampling Probability Sampling Systematic: A pre-determined system is followed. Procedure: 1. Have the total numbers of units in the population. 2. Decide the sample size. 3. Calculate the sampling ratio i.e. sample of 100 out of 1000= 1:10 370 out of 1600= 1:4.3 round it to to the nearest whole numbers and it will become 1:4. 4. Select randomly the first unit and interview every eve ry fourth unit that is 1:4.

Probability  Probability Sampling Probability Sampling Cluster Sampling: Sampling: Selection is made of clusters of  groups such as mohallas, apartment, buildings, villages, housing unit etc. When a list of the entire area is not available and is not physically possible to visit the entire area, one can divide the area into several equal size clusters.

Probability  Probability Sampling Probability Sampling Stratified Sampling: Sampling:  This This is done to compare different strata. Procedure: 1. Population is first divided into subgroups (Strata) according according to one or more characteristics e.g.; age, sex, economic status, religion etc. 2. Follow a random or systematic procedure procedure according to the available information. i nformation.

Non-Probability  Sampling Samp ling Accidental ( convenience ) Sampling: Sampling: * Sample is selected in a haphazard fashion. * Sample selected is unlikely to be representative. * The purpose of such sampling is usually less less cost, convenience etc. e.g. First ten patient in clinic, Students in library.

NON-PROBABILITY  SAMPLING • PURPOSIVE: Sampling done on the basis of some pre determined idea (clinical knowledge etc. ).The result of  such a sample can not be generalized. Example: • Samples from different age groups. • Sample of all hypertensive.

NON-PROBABILITY  SAMPLING

The strata of  • QUOTA SAMPLING : The

the population are identified & the researchers determine the proportion of elements needed from the various segments, eg: • If in a population of students 40% are female & 60% are males , then the researcher may decide for a sample size 50 , to select 20 females & 30 males .then he can use any type of probability or non-probability sampling procedures within the

REQUISITE OF A RELIABLE REQUISITE SAMPLE • EFFICIENCY  • REPRESENTATIVENESS REPRESENTATIVENESS • MEASURABILITY  • SIZE • COVERAGE • GOAL ORIENTED • FEASIBILITY  • COST- EFFECTIVENESS