Pop Goes the Sample
This term refers to the entire group of individuals you want information about.
What is a population?
In statistics, this is a flaw that leads to unrepresentative and/or inaccurate estimates.
What is bias?
This type of study follows individuals to gather future data.
What is a prospective study?
This principle of experimental design is used to reduce variation by grouping similar experimental units before randomly assigning treatments.
What is blocking?
In a recent poll of 1,500 randomly selected eligible voters, only 525 (35%) said that they did not vote in the last election. However, a vote count showed that 80% of eligible voters actually did not vote in the last election.
What type of bias most likely occurred in the poll?
What data are collected from every member of a population rather than a sample, it's called this.
What is a census?
This type of bias occurs when certain groups in the population are left out of the process of choosing the sample.
What is undercoverage bias?
These provide alternative explanations for trends between explanatory and response variables.
What are confounding variables?
This can be used to show a cause-and-effect relationship between two variables.
What is a controlled experiment?
Mr. Paguada conducted a study investigating the effectiveness of a new method for teaching a math unit. He recruited 80 students at a college and randomly assigned them to two groups. Group 1 was taught with the new method, and Group 2 was taught with the traditional method. Both groups were taught by the same teacher. At the end of the unit, an achievement test was administered and used to make a comparison of the two groups.
What is the response variable in the study?
The score on the achievement test.
In this type of sampling, every individual in the population has an equal chance of being selected.
What is a simple random sample (SRS)?
When people who are chosen for a sample cannot be contacted or choose not to participate, the results may suffer from this.
What is nonresponse bias?
These four principles are important to have an effective experiment design.
What are comparisons, random assignments, replication, and controls?
When both the subjects and researchers are unaware of who receives the active treatment or placebo.
What is a double-blind study?
A well-designed experiment should have which of the following characteristics?
1. Subjects assigned randomly to treatments
2. A control group or at least two treatment groups
3. Replication
1, 2, and 3
This sampling method randomly selects entire groups and includes all individuals within those groups in the sample. (also known for being internally heterogeneous)
What is a cluster sample?
This bias occurs when individuals in a sample give inaccurate answers, maybe because of wording, embarrassment, or misunderstanding.
A city planner is investigating traffic congestion at a certain intersection. To collect data, a camera will record the number of cars that pass through the intersection at different hours of the day and on different days of the week. What would best describe the type of investigation being conducted by the city planner?
The investigation is an observational study because treatments are not imposed.
When a subjects' belief of receiving an active treatment leads to a measured response, even though the treatment is actually inactive, this takes place.
What is the placebo effect?
A certain monthly magazine has both print and online subscribers. Print subscribers are people who pay to have the magazine physically delivered to them each month. Online subscribers are people who pay to have access to the electronic version of the magazine. The editors of the magazine want to study how online subscribers feel about the design of the electronic version, and they will gather data from a sample.
What is the population of interest?
What is the online subscribers?
At a certain clothing store, the clothes are displayed on racks. The clothes on each rack have similar prices, but the prices among the racks are very different. To estimate the typical price of a single piece of clothing, a consumer will randomly select four pieces of clothing from each rack. What type of sample is the consumer selecting?
A stratified random sample.
A school nutritionist was interested in how students at a certain school would feel after taking a nutritional supplement. The nutritionist selected a random sample of twenty students from the school to participate in the study. Participants were asked to keep a journal on how well they felt after taking the supplement each day. What possible source of bias is present in the method of data collection?
Response bias where responses were self-reported.
A researcher conducted an experiment to study the effects of an herbal supplement on the duration of the common cold. From a sample of 50 people who had a cold, the researcher assigned 25 people to take the supplement each day. The other 25 people were asked to drink water each day and were not given the supplement. The researcher recorded the number of days the cold lasted for each person. What are the experimental units of the study?
The sample of 50 people who had a cold.
A market search firm is studying the effects of price and type of packaging on sales of a particular product. Twenty-seven stores with shoppers of similar characteristics will be used in the study. The nine combinations of three price levels and three packaging types are the treatments of interest. Total sales of the product over a seven-week period will be recorded. Describe the best design to use for the study.
A completely randomized design. Randomly assign the nine combinations of price level and packaging type so that three stores use each combination.
Carla wants to investigate whether a person's political party affiliation causes the person to be more vocal about political issues. She plans to administer a survey to a large sample of people. Why would this method of data collection prevent Carla from reaching her goal?
Causation cannot be determined from a survey.