Unit 1 Section 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 Sampling  Systematic Sampling  Stratified Sampling  Cluster 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 2 nd 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 k th subject of the group.  If the group has a population p and you want to sample s subjects, p/s = k.  Example : Every 100 th 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

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