Unit 1Section 1.3 – Day 2

1.3: Sampling Techniques Sample – a part of a population used in

statistical studies.

An unbiased sample is one where each subject in the population has an equally likely chance of being selected.

A biased sample is one that is non representative of the entire population.

Sampling error is the difference between the results of a sample and those of a population.

Section 1.3

To obtain unbiased samples statisticians use four basic methods of sampling:

Random SamplingSystematic SamplingStratified SamplingCluster Sampling

Section 1.3

Random Sampling – every member of a population has a equal chance of being selected.

Previously, tables were used, now calculators are used.

Example: Nursing supervisors are selected using random numbers in order to determine annual salaries.

Section 1.3

Creating a Random Number List (on the TI) Press the Math button Use the arrow key to scroll right until you are on the PRB

menu Select option #5: randInt( Enter a starting value followed by a comma Enter an ending value followed by a comma Enter the number of values you wish to generate followed

by a closed parenthesis Press STO> Press 2nd then STAT Select L1

Your random numbers will be stored in L1 for use

Section 1.3

Stratified Sampling - selects by dividing the population up into groups by some characteristic that is important to the study, then sample from each group.

The groups are called strata. Each strata has equal representation in the

sample.

Example: Mail carriers in a large city are divided into 4 groups according to gender and whether they walk or drive. Then 10 are selected from each group and interviewed.

Section 1.3

Cluster Sampling- selects by dividing the population up into clusters and randomly selecting a few whole clusters as samples.

Clusters are naturally occurring groups. Different than stratified sampling, members

of each cluster are not grouped based on a characteristic.

Example: In a large school district, all teachers from two of the school buildings are interviewed.

Section 1.3

Systematic Sampling - selecting every kth subject of the group.

If the group has a population p and you want to sample s subjects, p/s = k .

Example: Every 100th hamburger manufactured is checked to determine its fat content.

Section 1.3

Other Sampling Methods Convenience Sampling - selects by

doing whatever is convenient for the researcher.

Sequential Sampling Double Sampling Multi-Stage Sampling

Section 1.3

Complete pages 24 - 26 #’s 23 - 36

Homework