2.  An observational study observes individuals and measures variable of interest but does not attempt to influence the responses.  Often fails due to lurking variables.  An experiment, on the other hand, deliberately imposes some treatment on individuals in order to observe their responses.  Is the preferred method of gaining knowledge since it allows us to control lurking variables. AP Statistics, Section 5.1, Part 12

3.  The entire group of individuals that we want information about is called the population.  A sample is a part of the population that we actually examine in order to gather information.  The units are the individuals on which the experiment is performed. AP Statistics, Section 5.1, Part 13

4.  Sampling involves studying a part in order to gain information about the whole.  Sample Frame is the actual set of units from which a sample has been drawn.  A census attempts to contact every individual in the entire population. AP Statistics, Section 5.1, Part 14

5.  Getting a portion of the population is not difficult.  Getting a good unbiased sample is difficult.  Creating a plan to do this is called “sample design”. AP Statistics, Section 5.1, Part 15

6.  Voluntary response sample (example: Call in opinion polls).  The problem with call in opinion polls is that the people who answer the polls tend to have strong opinions, especially strong negative opinions.  This sample is biased; this sample is not representative of the population. AP Statistics, Section 5.1, Part 16

7.  Convenience sample (example: Mall intercept interviews)  Convenience sampling may not get you access to all the people in the population.  Interviewers often avoid people who may make them feel uncomfortable.  This sample is biased; this sample is not representative of the population. AP Statistics, Section 5.1, Part 17

8.  The design of a study is biased if it systematically favors certain outcomes.  You are conducting an observational study on how many students in you class like your math teacher. State if the following is an example of:  Convenience sampling  Voluntary Response sampling  A good sampling design  Not even sampling AP Statistics, Section 5.1, Part 18

9. 9

10.  The easiest way to sample is to use a “simple random sample”  A simple random sample (SRS) of size n consists of n individuals from the population chosen in such a way that every set of n individuals has an equal chance to be the sample actually selected.  Avoids favoritism by the selectors and self- selection by the respondents. AP Statistics, Section 5.1, Part 110

11.  Choose an SRS in two steps:  Step 1: Label. Assign a numerical label to every individual in the population. ▪ Use the smallest amount of digits possible. ▪ Each label must contain the same amount of digits.  Step 2: Random Assignment. ▪ Random number table (Table B) ▪ Random number generator (RandInt in the TI-83) AP Statistics, Section 5.1, Part 111

12. AP Statistics, Section 5.1, Part 112

13. AP Statistics, Section 5.1, Part 113

14. AP Statistics, Section 5.1, Part 114

15. AP Statistics, Section 5.1, Part 115 A method of selecting members from a larger population according to a random starting point and a fixed, periodic interval. Typically, every “nth” member is selected from the total population. Ex: A cop at a checkpoint decides to speed check every 10 th car that passes him.

16.  To select a stratified random sample, first divide the population into groups of similar individuals, called strata. Then choose a separate SRS in each stratum and combine these SRSs to form the full sample. AP Statistics, Section 5.1, Part 116

17.  Convenience – it is easier to sample smaller groups.  Coverage – representation from each group is assured.  Precision – gives estimates closer to the true value of the population than an SRS. AP Statistics, Section 5.1, Part 117

18.  Good sampling technique uses random selection to reduce the possibility of bias. AP Statistics, Section 5.1, Part 118

19. AP Statistics, Section 5.1, Part 119

20.  Undercoverage occurs when some groups in the population are left out of the process of choosing the sample.  Surveys of households leave out homeless people, prison inmates and college dorms…  Opinion polls by telephone leaves out people with out phones, or are not listed…  Nonresponse occurs when an individual chosen for the sample can’t be contacted or does not cooperate. AP Statistics, Section 5.1, Part 120

21.  Response bias. Respondents may lie if they feel uncomfortable telling the truth.  The interviewer’s attitude towards some answers may influence how the respondents answer.  Ex. The interviewer wears an anti-abortion shirt while asking people about their views on abortion. AP Statistics, Section 5.1, Part 121

22.  Wording of questions. “It is estimated that disposable diapers account for less than 2% of the trash in today’s landfills. In contrast, beverage containers, third-class mail and yard wastes are estimated to account for about 21% of the trash in landfills. Given this, in your opinion, would it be fair to ban disposable diapers?” AP Statistics, Section 5.1, Part 122

23.  “Do you own or have you ever own a fur coat?” AP Statistics, Section 5.1, Part 123

24.  We want to make inferences about the population as a whole.  We can’t afford to talk to everyone.  Even though two samples, following the same design most probably will give us different results, those results are reasonable estimates of the population as a whole AP Statistics, Section 5.1, Part 124

25.  Properly designed samples avoid systematic bias, but their results are rarely accurate and vary from sample to sample. (Sampling Error)  Large random sample give more precise results than smaller sample. AP Statistics, Section 5.1, Part 125