Experimental Design (Sec. 1.3) Mr. Ricks Madison High School

Read the first 2 paragraphs on pg. 15 What is the goal of every statistical study? 1) Collect data 2) Use that data to make a decision The decision is only as good as the data! What do we mean by that?

Designing a Statistical Study Identify the variable of interest (the focus) and the population to study Develop a detailed plan for collecting data. (If you use a sample, make sure it is representative of the population.) Collect the data. Describe the data using descriptive statistics techniques. Interpret the data and make decisions using inferential statistics. Identify any possible errors.

Methods of Data Collection Census – a count or measure of an entire population Sampling – a count or measure of part of the population Simulation – the use of a mathematical or physical model to reproduce conditions of a situation or process Experiment- a treatment is applied to part of a population and responses are observed (often compared to a control group which may receive a placebo) Which of these 4 types applies to our study of the Teton watershed?

A survey is often used to collect data for a census or a sampling. The wording of questions can lead to biased results. School survey questions for accreditation? Other examples?

Which method of data collection? A study of the effect of reintroducing wolves into an ecosystem. A study of the effect of drinking milk on preventing cavities. A study of the heights of all quarterbacks in the NFL. A study of U.S. residents’ approval ratings of Congress.

For the following studies, identify the focus, population, and an appropriate method of data collection. A study of the effects of exercise on senior citizens. A study of the effects of radiation fallout on senior citizens.

Frog Story Activity Keep The Frog Story turned over until you are told to begin You will be given 4 minutes to count the number of “g”s in the story. Count both upper and lower case. When you are finished, record your number on question 1 on your answer sheet.

Frog Results Answer questions 2-4 on your handout Did everyone get the same answer? Why do you think the answers vary? With your team, take a few minutes and complete 5 and 6 on your handout.

Biased Samples A biased sample is not representative of the population. How could a sample be biased? Poor sampling technique, biased questions, etc. Watch for studies that produce a result that could benefit the sponsor. EX: A study sponsored by the United Dairymen of Idaho found that those who drink milk 3 times a day are less likely to develop muscle disease.

Sampling Techniques Random Sample Stratified Sample Cluster Sample Systematic Sample Convenience Sample

Random Sample Every member of the population has an equal chance of being selected. Show random number generator on calculator How could a random sample be generated for a population? Decide if you want the random selection to be with replacement or without replacement

Stratified Sample Divide the population into strata (subsets) and then randomly choose from each strata Members of each strata share similar characteristics such as age, gender, ethnicity, etc. This sampling method ensures that each segment of the population is represented

Cluster Sample Can be used when the population can be divided into naturally occurring subgroups having similar characteristics Each subgroup is called a cluster Select a cluster and take data from all members of that cluster Geographic grouping is common for this type What are some possible issues with this method?

Systematic Sample Each population member is assigned a number, placed in order, and every nth entry is taken for the sample. Is an easy method to use What problems could arise?

Convenience Sample Consists only of available people Commonly used for Project Citizen surveys Often leads to a biased study – Why? Not recommended

You are doing a study at your school to find student opinions about gun control. What technique is used if…? You select a class at random and question each student in the class. You divide the student population by grade level and question some students from each grade level. You assign each student a number and generate random numbers. You then question each student whose number is randomly selected. To conduct a meaningful survey at the high school what do you think would be the best way to gather data?

Random Rectangles Keep the page with rectangles upside down until you are told to look at it. You will be given 10 seconds to guess the average area of the rectangles on the given page Each small square is one square unit. Record your guess on your answer sheet.

Follow the instructions and complete the rest of your sheet Follow the instructions and complete the rest of your sheet. At the bottom of your paper answer these questions. Which of these sampling techniques do you think gave the best result? Why? What do you think could have been done with this technique to provide an even better result?

Assignment Sec. 1.3, pg. 20 #1-18,23-24 Ch. 1 Review, pg. 26 #1-12,17-26 and feel comfortable performing conversions Conversions/Ch. 1 Quiz next time