At a high school, the registrar lists all 840 students by ID, randomly chooses one of the first 20 IDs, then surveys every 20th student. No treatment is imposed; students know the lunch survey measures menu preferences. What sampling method is this?

To study homework time, a counselor separates the 1,200-student roster by grade and randomly selects 25 students from each grade. No treatment is imposed; students know the survey measures minutes of homework per night. What sampling method is used?

An assistant principal lists the school's 48 homerooms, randomly chooses 6 homerooms, and surveys every student in those rooms. No treatment is imposed; students know the survey measures opinions about phone rules. What sampling method is used?

To estimate online quiz use, a district lists all 310 teachers, numbers them, and uses a random number generator to choose 40 teachers. No treatment is imposed; teachers know the survey measures quiz use. What sampling method is used?

A hospital team groups 900 nurses by shift, then randomly selects 30 nurses from each shift for a safety survey. No treatment is imposed; nurses know the survey measures reporting habits. What sampling method is used?

A city lists 75 apartment buildings, randomly selects 10 buildings, and asks every tenant in those selected buildings about recycling. No treatment is imposed; tenants know the survey measures recycling behavior. What sampling method is used?

At a factory, a supervisor lists parts in production order, randomly selects one of the first 50 parts, and inspects every 50th part after that, measuring each chosen part's length in millimeters. What sampling method is used?

A school newspaper posts an online poll asking readers to click if they support later start times; 430 readers choose to answer. No treatment is imposed; the poll measures opinions. What kind of bias is the main problem?

A principal surveys only students in honors English classes about a rule meant for the whole school. No treatment is imposed; students know the survey measures support for the rule. What kind of bias is the main problem?

A coach asks, 'Don't you agree sugary drinks hurt performance?' before recording athletes' drink choices. No treatment is imposed; athletes know the survey measures nutrition opinions. What kind of bias is the main problem?

A district randomly selects 200 parents for a transportation survey, but only 38 parents return it. No treatment is imposed; parents know the survey measures bus satisfaction. What kind of bias is the main problem?

A city surveys households from a landline phone directory about bus routes, excluding homes with only cell phones. No treatment is imposed; respondents know the survey measures transit needs. What kind of bias is the main problem?

A teacher asks students face-to-face, with names on the form, whether they copied homework. No treatment is imposed; the survey measures admitted cheating. What kind of bias is the main problem?

Researchers record sleep hours and semester GPA for 90 students who follow their usual schedules. Students know the study measures sleep and grades. What kind of study is this?

A tutoring company randomly assigns 120 students to use either an app or paper practice for two weeks. Students know their assigned practice type, and the company measures exam scores. What kind of study is this?

Doctors record the usual diets and blood pressure of 150 adults at one clinic. Patients know the study measures food habits and blood pressure. What kind of study is this?

An agriculture class randomly assigns tomato plants to one of three fertilizer brands. Students know the assigned brand, and they measure each plant's height in centimeters after six weeks. What kind of study is this?

A department randomly assigns 16 Algebra 2 classes to use either daily review or weekly review. Teachers know the schedule assigned, and the department measures unit exam scores. What kind of study is this?

A bakery randomly assigns 60 loaves to bake at 180, 200, or 220 degrees Celsius. Bakers know the temperature, and they measure each loaf's crust thickness in millimeters. What is the response variable?

A clinic randomly assigns 120 patients to text reminders or phone reminders for appointments. Patients know their reminder type, and the clinic records whether each patient misses an appointment. What are the experimental units?

A greenhouse randomly assigns tomato plants to receive 200, 400, or 600 milliliters of water daily. Workers know the watering amount, and they measure plant height after a month. What is the treatment factor?

An online course randomly assigns 80 students to a 5-minute lesson or a 12-minute lesson. Students know the lesson length, and the course records quiz scores. What is the purpose of random assignment here?

A lab randomly assigns 160 phone batteries to four charger brands, with 40 batteries on each brand. Technicians know the brand and measure charge after one hour. What design principle is shown by using many batteries per brand?

A nutrition study randomly assigns students to a sports drink or plain water before a workout. Students know their drink, and researchers measure heart rate recovery in beats per minute. What role does the plain-water group play?

In a trial of a new allergy spray, patients receive real spray or inactive spray, and neither patients nor symptom-recording nurses know who received which. The researchers measure daily symptom scores. What feature is this?

A pill study randomly assigns patients to a real medicine or a sugar pill that looks the same. Patients do not know which pill they receive, and researchers measure headache pain. What is the sugar pill called?

In a skin-cream study, patients do not know whether they receive the new cream or the old cream, but the doctors applying it do know. Researchers measure redness after a week. What feature is this?

A school compares a new math program taught only in morning classes with the old program taught only in afternoon classes. Teachers know the program, and exam scores are measured. What problem is created by time of day?

A pain study includes an inactive pill because people may report less pain simply from expecting treatment. Patients do not know their pill type, and researchers measure pain ratings. What issue is the inactive pill meant to address?

A trainer studies two stretching routines with sprinters and distance runners. She first separates athletes by event, randomly assigns routines within each event group, and measures sprint time. What design is this?

A shoe company has each runner try Shoe A and Shoe B on two similar 5-kilometer runs in random order. Runners know the shoe, and the company measures run time. What design is this?

Researchers recruit 30 pairs of twins for a study of two breakfast plans. Within each twin pair, one twin is randomly assigned to each plan, and energy level is measured. What design is this?

A factory tests three lubricants on machines of two model types. Engineers separate machines by model, randomize lubricants within each model group, and measure energy use. What role does machine model play?

A researcher randomly assigns all 80 seedlings to one of two light colors without first grouping them by variety. Workers know the light color, and height is measured. What design is this?

To select 4 of 30 students numbered 01 through 30, a teacher reads two-digit groups: 52 18 07 33 18 24 02. She skips repeats and invalid numbers. Which students are selected in order?

A researcher selects 3 of 20 lab stations numbered 01 through 20 using two-digit groups: 05 27 14 00 19 14. She skips repeats and invalid numbers. Which stations are selected in order?

To choose 5 of 50 club members numbered 01 through 50, a student reads two-digit groups: 49 62 03 50 03 17 08. Repeats and invalid numbers are skipped. Which members are selected in order?

A district randomly samples ninth graders, then randomly assigns them to use a planner app or a paper planner for six weeks. Students know their planner type, and grades are measured. What conclusion does this design support?

Volunteers from one gym are randomly assigned to two warm-up routines for a month. Participants know their routine, and researchers measure injury counts; one routine has fewer injuries. What conclusion does this design support?

A city randomly samples adults and records their usual coffee intake and average sleep hours without assigning any intake. Respondents know the survey topic, and the study finds an association. What conclusion does this design support?