1 CLASS LECTURE NOTES - What is Applied Statistics ...

Stratified sample: In cases where population under study may be viewed as comprising different
groups (stratas) and where elements in each group are more or less homogeneous, we randomly
select elements from every one of the strata.
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Convenience sample: samples are taken based on convenience of the experimenter.
Systematic sample: units are taken in a systematic way such as selecting every 10 th item after
selecting the first item at random.
HOW TO USE SAMPLES?
- Samples should represent the population.
- Random sample obtained will not always be an exact copy of the population.
- Thus, there is bound to be some error:
1. Random or unbiased error: This is due to the random selection of the sample and the mean
of such error will be 0 as positive deviation and negative deviation cancel out. This random error
is also referred to as random deviation and is measured by the standard deviation of the estimator.
2. Non-random or biased error: this occurs due to several sources such as human, machines,
mistakes due to copying or punching, recording and so on. Through careful planning we should
try to avoid or minimize this error.
EXPERIMENTS USING MINITAB
We will illustrate the concepts of sample, sampling error, etc with practical data using MINITAB.
See class lecture for details.