For example, we are interested in the average test score in a large Biometry class of size, say, 80. A sample of size 10 scores from this resulted in an average test score of 75. If the average test score for the entire 80 students (the population) is 72, then the sampling error is: 75 - 72 = 3. (9) Sampling Variance - a measure of the divergence of the estimate from its expected value. Lecture Number 4 Introduction to Sampling Methods October 28, 2016 9 / 35
Steps in Conducting a Sample Survey The main steps that are involved in a sample survey are: (1) Statement of objectives; (2) Definition of the population to be studied; (3) Determination of the sampling frame and sampling units; (4) Selection of proper sampling design; (5) Determining the sample size; (6) Organisation of field work; (7) Collection of data (i.e., conducting the survey); (8) Summary and analysis of data. There are many sampling designs/schemes/methods available. The choice between sampling methods depends on: (1) the nature of the problem or investigation; (2) the availability of good sampling frames; (3) the budget or available financial resources; (4) the desired level of accuracy; and (5) the method by which data will be collected, such as questionnaires or interviews. Lecture Number 4 Introduction to Sampling Methods October 28, 2016 10 / 35
Types of Sampling Methods A sampling method is a specific technique used to select sampling units that constitute a sample. Sampling methods are generally grouped into two categories; probability and non-probability sampling methods. (1) Probability Sampling is the method of selecting samples according to certain laws of probability in which each unit in the population has some definite probability of being selected in the sample. (2) Non-probability Sampling is a method of selecting samples in which the choice of selecting of sampling units depends entirely on the discretion or judgement of the sampler. The method is mainly used for opinion surveys but cannot be recommended for scientific use as it is subject to the drawbacks of prejudice and bias of the sampler. It is also not possible to compute the degree of precision of the estimates from the sample values. Lecture Number 4 Introduction to Sampling Methods October 28, 2016 11 / 35
Types of Sampling Methods There are four main types of probability sampling methods that are standard across disciplines: (1) Simple Random Sampling; (2) Systematic Sampling; (3) Stratified Sampling; and (4) Cluster Sampling. In addition to the four, we also have; (5) Multi-Stage Sampling; (6) Multi-Phase Sampling; and (7) Probability Proportional to Size (PPS) Sampling Non-Probability Sampling methods include: (1) Convenience Sampling; (2) Judgement (purposive) Sampling; (3) Snowball Sampling; and (4) Quota Sampling. Lecture Number 4 Introduction to Sampling Methods October 28, 2016 12 / 35
Simple Random Sampling This is a method of selecting n units out of a population of size N by giving equal probability (chance) to all units, or a sampling procedure in which all possible combinations of n units that may be formed from a population of N units have the same probability of being selected.
- Fall '18
- F. TAILOKA
- representative, Basic Concepts of Sampling