A fertilizer study first sorts 60 garden plots into sandy, loamy, and clay soil groups, then randomly assigns half of each soil group to fertilizer A and half to fertilizer B. What design did the researcher use?

A tutoring study puts 90 students' names in one list and uses a random-number generator to assign 45 to online tutoring and 45 to in-person tutoring, with no grouping before assignment. What design is this?

A reading study pairs students with similar pretest scores; within each pair, one student is randomly assigned to a new app and the other to paper practice. What design did the study use?

A sunscreen study first groups 120 volunteers by fair, medium, or dark skin tone, then randomly assigns each skin-tone group evenly to sunscreen X or sunscreen Y. What design is this?

A packaging study randomly assigns 50 identical cereal boxes to label A and 50 to label B, without sorting boxes or stores into groups first. What design did the company use?

A study of two ankle braces matches athletes in pairs by sport and prior injury history; a coin flip assigns one athlete in each pair to each brace. What design is this?

A delivery study sorts 72 orders into downtown, suburban, and rural address groups, then randomly assigns half of each address group to route software A and half to route software B. What design is this?

A music study randomly assigns 80 volunteers to hear either slow background music or fast background music while solving puzzles, with no sorting before assignment and one music condition per person. What design is this?

A diet study pairs adults with similar age, sex, and starting weight; within each pair, one adult is randomly assigned to diet A and the other to diet B. What design did the study use?

A shoe trial sorts 80 runners into four groups by weekly distance run, then randomly assigns shoe model A or B within each distance group. What variable did the study block on?

A tablet study groups 120 students by grade level before randomly assigning each grade group to tablet lessons or paper lessons. What variable did the researchers block on?

A farm experiment sorts 48 fields into low, medium, and high soil nitrogen groups, then randomly assigns irrigation plans within each group. What variable was used for blocking?

A reading-app experiment places 96 students into groups by baseline reading score, then randomly assigns app A or app B within each score group. What is the blocking variable?

A pain-cream trial groups 75 patients by injury location before randomly assigning cream A or cream B within each location group. What did the trial block on?

A math-curriculum experiment groups classrooms by teacher experience level, then randomly assigns each experience group to curriculum A or B. What is the blocking variable?

A blood-pressure study sorts adults into age bands before randomly assigning two exercise plans within each band, because age may affect blood pressure change. What does blocking by age accomplish?

A seed experiment groups pots by shade level before randomly assigning fertilizer A or B within each shade group. Why is shade level used as a block?

An online-lesson study groups students by prior quiz score, then randomly assigns lesson format within each group. What is the purpose of blocking on prior quiz score?

An inhaler study groups patients by clinic, then randomly assigns inhaler A or B within each clinic because clinics may treat patients differently. What does the blocking accomplish?

A sauce taste test sorts tasters by how often they eat spicy food, then randomly assigns sauces within each group. What does this blocking do?

In a keyboard study, each of 30 typists types the same passage on layout A and layout B, with each typist's order decided by a coin flip. What design is this?

A treadmill study has each runner complete a 2 km run on treadmill A and a 2 km run on treadmill B on separate days, with order randomly assigned. What design is this?

A calculator-interface study has every student solve one problem set with interface A and one with interface B, with the order randomly chosen for each student. What design did the study use?

A radiology study has each doctor read the same 40 scans on display A and display B, with the display order randomized for each doctor. What design is this?