Do now Which of the following is an observational study and which is an experiment? A Stat instructor announces a study session to be held the night before a test. The instructor lists the students who attended the session and compares their scores to the remaining Stat students’ scores. To determine whether a review session will improve his students’ test scores, a Statinstructor divides his class into two groups. He then requires one group to attend a study session and compares the test results of each group.

Lesson 3.2 Sampling: Good and Bad

Describe how convenience sampling can lead to bias. Objectives Describe how convenience sampling can lead to bias. Describe how voluntary response sampling can lead to bias. Explain how random sampling can help to avoid bias.

It is well known that different authors use different styles and word choice.  It turns out that the average word length is fairly consistent for each author and can be used as a way to distinguish one author from another.  Since we know for sure that Beyonce wrote the lyrics for all of the Destiny’s Child songs (average word length 3.64), we should be able to determine her possible authorship of “Crazy in Love” by finding the average word length.

When her hit “Crazy in Love” came out, people started questioning whether or not she had written the lyrics. In a Vanity Fair article, Beyonce came back at them: “‘Crazy in Love’ was really hard to write because there was so much going on … I mean, I had written — what? —seven, eight number one songs with Destiny’s Child, in a row.”

definitions Choosing individuals from the population who are easy to reach results in a convenience sample.

definitions A voluntary response sample consists of people who choose themselves by responding to a general invitation. Random sampling involves using a chance process to determine which members of a population are included in the sample.

Definitions The design of a statistical study shows bias if it would consistently underestimate or consistently overestimate the value you want to know

Lesson 3.3 Simple Random Samples

Use simulation to test a claim about a population proportion. objectives Describe how to obtain a simple random sample using slips or paper or technology. Explain the concept of sampling variability and the effect of increasing sample size. Use simulation to test a claim about a population proportion.

Definitions A simple random sample (SRS) of size n is chosen in such a way that every group of n individuals in the population has an equal chance to be selected as the sample.

Important Ideas Sampling Variability: each sample is different, some give estimates that are too high, some too low Increase sample size- decrease variability SRS – simple random sample Slips of paper – identical size, mix well Random number generator: ignore repeats