Download Section 1.2

Section 1.2
Where does data come from?
Census: Obtaining data from an entire population of interest
Two methods other than a census
1. Sampling
2. Experimentation
What is important for a sample? It needs to be a representative sample.
Probability Sampling: is used in modern sampling procedures. A random
device-such as a tossing a coin, using a table of random number
generators, or using a random number generator.
This book will use one particular sampling procedure for inferential studies
and that is simple random sampling.
Simple random sampling: A sampling procedure for which each possible of
a given size is equally likely to be the one obtained.
Simple random sample: A sample obtained by simple random sampling.
Two types of simple random sampling.
Simple random sampling with replacement: A member of the population
can be selected more than once.
Simple random sampling without replacement: A member of the population
can be selected at most once.
Exercise
Simple random samples
Selecting four Beenie Baby Bears from a group of five.
How many different groups of four from the population of five could there
be? Use the combinations formula
n Cr

n!
n-r !  r !
Random Number Table: s a table of randomly chosen digits
How do we use this?
1. Number the objects or individuals in the population from 1 to N where
N is the total number of objects in the population.
2. If N is a two digit number, then two digits will be used, If N is a three
digit number, then three digits will be used.
3. The sample size is n.
4. Close your eyes and hit the chart.
5. Go down (or across) the table and find n one, two, or three digit
numbers (depending upon N) between 1 to N
6. Don’t repeat the numbers (Sampling without replacement).
Exercises