Types of Samples
What is a sample?
A small group taken from a population
What are the names of the type of experimental designs that we learned in class?
Block design
Single/Double blind
Matched Pairs
The term used to describe the individuals in an experiment.
Subjects/experimental units
Describe the difference between a parameter and a statistic
Parameter: A number that describes the entire population (true proportion/true mean)
Statistic: A number that describes a sample (sample proportion/sample mean)
A researcher is studying the effect of two different diets on weight loss. Participants are grouped by gender (male and female), then within each group, they are randomly assigned to one of the two diets. What type of experiment is this?
Block design
Which is an example of a biased sample?
- Randomly selecting from all students
-Choosing only students in a statistics class
- Using a national database
-Conducting a blind survey
-Choosing only students in the statistics class
A researcher is testing a new study technique. She randomly assigns 50 students to either use flashcards or take practice quizzes. She does not tell the students which method is expected to perform better, and the person grading the tests does not know which method each student used.
What type of experimental design does this represent?
Double blind experiment
The variable that researchers manipulate in an experiment to observe its effect is called what?
Explanatory Variable
The number that describes a sample (sample proportion/sample mean)
Statistic
Students use flashcards or an app, and teachers compare test scores. What is the treatment?
Study method (flashcards vs. app)
A student stands outside the library and surveys the first 20 people who walk by about their study habits. What type of sampling is this?
Convenience Sample
To test the effectiveness of a new allergy medication, researchers first divide participants into groups based on the severity of their allergies (mild, moderate, severe). Then, within each group, participants are randomly assigned to receive either the new drug or a placebo.
What type of experimental design is this?
Block design
This type of variable, also called a confounding variable, may affect the outcome but is not the focus of the experiment. Researchers try to control or block for these variables.
Lurking Variable
A teacher wants to know the average test score of all 100 students in the school. She takes a random sample of 20 students and finds their average test score is 82.5.
Parameter or Statistic?
Statistic
You are studying the effect of three different fertilizers and two watering schedules on tomato plants. You use 4 plants per treatment.
A polling company surveys public transportation riders by randomly selecting bus routes, and then surveying everyone on those routes during peak hours. What type of sample is this? What is the potential bias?
Bias: Only peak hour riders are included in the sample
In a study, each participant receives both the new treatment and a placebo at different times, with a break in between. The order of treatments is randomized, and the participant’s response to each is compared.
What is this type of experimental design called?
Matched Pairs Design
A researcher wants to test whether a new tutoring program improves students’ math scores. She randomly assigns some students to the tutoring program and others to a control group with no tutoring. After 3 months, all students take the same standardized math test.
What is the the response variable?
Students' math scores
In a medical trial of a new drug, all 150 participants were studied, and the average recovery time was 5.2 days.
Parameter or Statistic
Parameter
Researchers want to study if listening to classical music affects stress levels. They randomly assign participants to listen to classical music or sit in silence for 30 minutes. Then they measure participants' heart rates.
Find the:
Explanatory Variable
Response Variable
Lurking Variable (if any)
Experimental Units
Treatment
Response Variable: Total weight of tomatoes harvested
Explanatory Variable: Type of fertilizer (A or B) Subjects/Experimental Units: 40 tomato plants Treatment: Fertilizer A vs. Fertilizer B
Lurking Variable: Soil quality, sunlight, watering schedule
A school district wants to study whether a new vegetarian lunch menu increases student satisfaction.
Sampling:
The district selects 3 high schools at random from a list of 12. From each selected school, they survey every student who eats school lunch that day.
Experimental Design:
Within each selected school, students are split into two groups based on whether they usually eat meat or not. In each group, students are randomly assigned to either receive the regular lunch menu or the new vegetarian lunch menu for a week. At the end, all students complete a satisfaction survey.
1. What sampling method is used?
2. What experimental design is used?
3. Is this an experiment or observational study?
1. Cluster
2. Block design
3. Experiment
In a clinical trial, neither the participants nor the doctors know who is receiving the treatment or the placebo, but the researchers analyzing the results do know.
What type of blinding is this, and why is blinding used in experiments?
Double blind and blinding is used to reduce bias between participants and doctors.
A health researcher wants to study the effect of a new diet on cholesterol levels. She recruits 100 adults and randomly assigns 50 to follow the new diet and 50 to continue their regular eating habits. After 6 months, she measures each participant’s cholesterol level.
Find the: Explanatory variable, response variable, treatment, individuals, and possible lurking variables.
Explanatory Variable: Type of diet
Response Variable: Participants’ cholesterol levels measured after 6 months.
Treatment: New diet (treatment group), Regular eating habits (control group)
Individuals: The 100 adults participating in the study.
Lurking Variables: Participants’ exercise habits, Genetics or family history of cholesterol problems, Age or gender, Use of cholesterol-lowering medications
A researcher is studying the sleep patterns of teenagers in a large city with 18,000 high school students. She collects data from a random sample of 600 students and finds that the mean amount of sleep per night is 6.3 hours. She then reports this value as the average for all high school students in the city in her article. Parameter or Statistic? What errors did the researcher make in her conclusion?
Statistic
The researcher incorrectly treats the statistic as a parameter by reporting it as the average for all of the high school students in the city.
A school wants to randomly choose 5 students out of 50 total, to receive a gift card. Use line 112 to randomly select the 5 students.
04,11,19,35,27