Review of Chapters 8-12, 14-15 (Midterm #2) Review of major concepts, topics, and definitions covered in Chapters 8-12 and 14-15 (everything covered on the second midterm). Includes highlighting and equations to make important points clear and noticeable.
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Chapters 8-12, 14-15 02/05/2012 01:11:00
Chapter 8 - Sampling
When sampling, there are two key terms that you must know:
Population is the entire group of individuals we want information
Sample is the part of the population we actually collect info from
A sample selected by taking members of the population that are easiest to
reach is called a convenience sample and often produce unrepresentative
data. A system error (favouring of a particular outcome) caused by a bad
sampling design is known as bias.
SIMPLE RANDOM SAMPLES (SRS)
- A way for impersonal chance to choose the sample (removes bias)
- Gives all individuals an equal chance of being chosen
- Gives all possible samples an equal chance of being chosen
TABLE OF RANDOM DIGITS
A long string of digits 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 with these two properties:
- Each entry is equally likely to be any of the 10 possible digits
- Entries are independent of each other
When using the table, the steps are as follows:
1. Label, give each member of population numerical value of same length
2. Table, read successive groups of digits of chosen length
STRATIFIED RANDOM SAMPLE
First classify the population into groups of similar individuals called strata,
then choose separate SRS in each stratum and combine these.
Eg. children is one strata and parents is another
Multistage samples take this idea even further and simply involve many
layers of SRS to create the final sample.
Eg. choose area code, phone number, household member
CAUTIONS ABOUT SAMPLE SURVEYS
Undercoverage occurs when some groups in the population are left out of
the process of choosing the sample (perhaps a full list of population wasn’t
available). Nonresponse occurs when an individual chosen for the sample
can’t be contacted or refuses to participate.
Chapter 9 - Experiments