Random samples

are selected by using chance methods or random numbers.

ex random samples

Number each object in the population; Place the numbered card in a box and mix them; Select as many card as needed to form the sample.

Systematic samples

Numbering each object in the population; Selecting every Kth value.

ex Systematic samples

suppose there are 2000 students in an elementary school and a sample of 50 students is needed. Solution: give a number to each student. then find k=2000/50=40 and every 40th student would be selected. Choose randomly the 1st student from 1 through 40.

Stratified samples

are selected by Divide the population into groups (X { typically: race, age, gender, religion, education}) Obtain a random or systematic sample of each X; Put together the samples obtained in the previous step for your ________.