1.2 Random Samples

A simple random sample of n measurements from a population is a subset of the population selected in a manner such that a) every sample of size n from the population has an equal chance of being selected AND b) every member of the population has an equal chance of being included in the sample. *Guided Exercise 3 p.12

 Use a random-number table Table 1 in the Appendix p. A1 Sampling Techniques  Assign each object a number, write numbers on cards, mix up cards, choose random cards 1)Random sampling

Another use for a random-number table is in simulation. A simulation is a numerical facsimile or representation of a real-world phenomenon. *Guided Exercise 4 p.14

2)Stratified sampling—the population is broken down into groups/classes (strata) and a random sample is chosen from each strata i.e. Population: All ASFA students Strata: CW, DA, MS, MU, VA, TA or 7 th, 8 th, 9 th, 10 th, 11 th, 12 th grades or male students, female students Other Sampling Techniques

3)Systematic sampling—assumes the elements of the population are arranged into some natural order. Select a random starting point, then choose every k th element. i.e. Population: People lined up to purchase concert tickets Sample: choose every 5 th person in line (with the starting person being one of the first 5 people in line) *Easy way to draw a sample, but should not be used when the population is cyclic in nature (fabric mill/loom) Other Sampling Techniques cont’d

4)Cluster sampling—divide demographic area into sections. Randomly choose sections or clusters. Each member of a cluster is included in the sample.  Used by government agencies and private research organizations 5)Convenience sampling—uses data or results that are conveniently or readily available.  High risk of bias Other Sampling Techniques cont’d

p. 17 #1 –9 odd Classwork