Samples

Assist. Prof. Dr. Mohammed Al-dujaili

Department of Ceramics Engineering and Building Materials
Faculty of Materials Engineering
University of Babylon
2016-2017
Lecture 2
Stage: Second
Subject: Engineering Statistics
Samples
In statistics and quantitative research methodology, a data sample is a set of data collected and/or selected from a statistical population by a defined procedure. The elements of a sample are known as sample points, sampling units or observations.
Concept of Sample
Recall that statistical inference permits us to draw conclusions about a population based on a sample.

A Samples and the methods of samples collection
Three of the most popular methods are:
•Direct Observation
•Experiments
•Surveys
Systematic sampling
Is a type of probability sampling method in which sample members from a larger population are selected according to a random starting point and a fixed periodic interval. This interval, called the sampling interval, is calculated by dividing the population size by the desired sample size

Multi-stage sampling
Multistage sampling can be a complex form of cluster sampling because it is a type of sampling which involves dividing the population into groups (or clusters). Then, one or more clusters are chosen at random and everyone within the chosen cluster is sampled.

Quota sampling
In quota sampling, a population is first segmented into mutually exclusive sub-groups, just as in stratified sampling. Then judgment is used to select the subjects or units from each segment based on a specified proportion. For example, a burn may be to sample 20 and 25 between 1000 and 1100. This means that students can put a demand on who they want to sample (targeting)

Types of Non-Probability Sampling

A purposive sample
Is a non-probability sample that is selected based on characteristics of a population and the objective of the study. Purposive sampling is also known as judgmental, selective, or subjective sampling.