Section 1.4 Check-Up During a show on MTV, the host asks viewers to text one number if they like the song “Call me Maybe” and to text a different number if they dislike it. 12,355 viewers responded with 74% saying they liked the song. With such a large sample and a percentage so far above 50%, is it safe to assume that the majority of Americans like the song?

Collecting Sample Data Section 1-5

There is no way to salvage data that wasn’t properly collected There is no way to salvage data that wasn’t properly collected. No matter how much you are willing to calculate, the data is useless.

General Ways to Collect Data Observational Study: Observe, but do not modify subjects Experiment: Apply a treatment to the subjects and observe the effects

Try It Out! Observational Study or Experiment? You call 12 people and ask them what medicine they prefer to give their children when they have a cold You bring in 12 children with colds and give 6 of them medicine and the other 6 a placebo. You track how many were better within 2 days.

Something Different … Activity 1 I will row a die to select a row, I will then roll the die again to select a student in the row to ask a survey question to. How representative were we? Does every student have the same chance of being selected? Does every possible group of 6 students have the same chance? This represents a random sample but not a simple random sample

Something Different… Activity 2 I will call on every 4th student to ask a survey question to. How representative were we? Did everyone have the same chance of being selected? Did every possible group of 6 students have the same chance? This represents both a random sample and a simple random sample

Random vs. Simple Random Random Sample: Everyone in the population has the same chance of being selected for observation Simple Random Sample: Each group of n subjects has the same chance of being selected for observation

Simple, Random, Both, or Neither? You are considering all teachers in a district. You randomly select 3 of the 12 schools in the district and survey every teacher in the school. You are considering all upper class students in a school. You randomly select 75 of the 800 juniors and 75 of the 750 seniors. You are considering all 2500 students in a school. You use a random number generator to randomly select 20 numbers from 1-2500 and choose the 20 students who correspond to those numbers.

Experiment Techniques Blinding: A technique in which the subject doesn’t know whether he or she is receiving a treatment or a placebo. Double Blind: Means that a blinding technique occurred at two levels: (1) The subjects do not know whether they are receiving a treatment or a placebo, and (2) The experimenters do not know which subjects are receiving a treatment or a placebo. Placebo Effect: An effect that occurs when an untreated subject reports an improvement in symptomes.

Mini Project In groups … Develop a quick skit to present to the class that demonstrates one of the following experiment techniques: A non-blind experiment A blind experiment A double blind experiment The placebo effect

Homework Pg. 36 #21-26

Collecting Sample Data Section 1-5

Warm-up 20 students will be randomly selected. On your own, find the average length of the 20 straws we pulled out of the box. Then find the average of all the straws in the box. Check your results with your neighbor. Did our sample provide an average that was close to the true population average? Why or why not? Was my sample simple, random, neither, or both?

Popular Sampling Techniques Systematic Select every kth person Convenience Use data that is easy to obtain Stratified Subdivide population into subgroups of people in similar demographics and randomly select a sample from each group Cluster Divide the population into sections. Randomly select some of the sections and choose all members in the section.

Randomization An important part of experiment/observational study design is randomization. There are lots of ways to randomly select a subject: Random Number Generator Draw Sticks/Cards/Numbers Rolling a dice Flipping a coin

Homework p.35: 6, 8, 10, 14, 15, 18