Review: Correlation and causation Math 075

Correlation Versus Causation Squares Talk in your groups to determine if each scenario represents Causation or Correlation. Be prepared to share out.

Collecting Data-Sampling Module 5

Sampling Plan Describes exactly how we will choose the sample A sampling plan is biased if it favors certain outcomes.

How to sample badly Sample Badly with Volunteers: In a voluntary response sample, a large group of individuals is invited to respond, and all who do respond are counted. Voluntary response samples are almost always biased, and so conclusions drawn from them are almost always wrong. Voluntary response samples are often biased toward those with strong opinions or those who are strongly motivated. Since the sample is not representative, the resulting voluntary response bias invalidates the survey.

How to sample badly Sample Badly, but Conveniently: In convenience sampling, we simply include the individuals who are convenient. Unfortunately, this group may not be representative of the population. Since the sample is not representative, the resulting convenience sampling bias invalidates the survey.

How do you eliminate bias? Simple Random Sample: Everyone in the population has an equal chance of being selected.

How does this work? Let’s take a look at the Gettysburg Address…

Cluster Sample Cluster Sample – Divide the population up into small groups that represent the population. Then choose groups (randomly) and get data from everyone in just those groups randomly selected. Cluster can be good or bad depending on if groups are chosen randomly.

Stratified Sample Stratified sample – Break the population into a few large groups that are different in some important way. Then (randomly) pick individuals from each group to form samples. Comparison studies. Can be good or bad depending on if individuals are chosen randomly.

Systematic Sample Systematic sample – Use a system to choose people in your data set. Can be good or bad depending on if you use randomization.

Practice ...identify method of collecting data & explain if the sampling method will represent the population. The COC Admissions department wants to see how many students would be in favor of using a new program to register for classes. They put a link on their website so that any students that wants to try out the program can. The students can then take a survey and say how well they like the new system. Rick works for a sports equipment manufacturing company. He separates all the employees into men and women, and then chooses 28 women and 30 men to ask if they want changes to their medical insurance coverage. Michelle, a teacher at Valencia High, wants to see how many students at Valencia High school will be attending COC. She gives the students in her U.S. History class a questionnaire to fill out that asks where they will be attending college.

Practice ...identify method of collecting data & explain if the sampling method will represent the population. Jamie is working at the Republican recruiting committee in Newhall. She is curious how many people that live in Newhall will vote for the Republican candidate in the next election. She obtained an alphabetical list of all the residents in Newhall and numbered them. She then used the computer to generate random numbers to decide which people to question about their voting preferences. Rachael works at the Democrat recruiting center in Northridge. To determine what percent of people will vote for the Democratic candidate, she obtains a list of all residents of Northridge and decides to ask every 50th person on the list. Mike is trying to take an opinion poll about how people in Los Angeles would feel about raising taxes in order to have a professional football team. He randomly selects 45 streets in Los Angeles and asks every person living on those streets. The principal of an elementary school requires all parents or guardians to fill out a questionnaire and provide proof of whether or not their child is up to date with their vaccinations.

Random Rectangles

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