When we take a census, we attempt to collect data from
every individual in the population
A study of treatments for angina (pain due to low blood supply to the heart) compared bypass surgery, angioplasty, and use of drugs. The study looked at the medical records of thousands of angina patients whose doctors had chosen one of these treatments.
We can't conclude that drugs prolong life because the groups might differ in ways besides the treatment.
Tonya wanted to estimate the average amount of time that students at her school spend on Facebook each day. She gets an alphabetical roster of students in the school from the registrar's office and numbers the students from 1 to 1137. Then Tonya uses a ra
it gave every possible sample of size 30 an equal chance to be selected
Consider an experiment to investigate the effectiveness of different insecticides in controlling pests and their impact on the productivity of tomato plants. What is the best reason for randomly assigning treatment levels (spraying of not spraying) to the
Random assignment will tend to average out all other uncontrolled factors such as soil fertility so that they are not confounded with the treatment effects
Researchers randomly selected 1700 people from Canada who had never suffered a heart attack and rated the happiness of each person. Ten years later, the researchers followed up with each person and found that people who were initially rated as happy were
Happier people in the study were less likely to have heart problems.
A TV station wishes to obtain information on the TV viewing habits in its market area. The market area contains one city of population 170,000, another city of 70,000, and four towns of about 5,000 residents each. The station suspects that the viewing hab
A stratified sample from the cities and towns in the market area
Bias in a sampling method is
any difference between the sample result and the truth about the population that tends to occur in the same direction whenever you use this sampling method
You wonder if TV ads are more effective when they are longer or repeated more often or both. So you design an experiment. You prepare 30-second and 60-second ads for a camera. Your subjects all watch the same TV program, but you assign them at random to f
This is a completely randomized design with two explanatory variables (factors)
Can texting make you healthier? Researchers randomly assigned 700 Australian adults to either receive usual health care or usual health care plus automated text messages with positive messages, such as "Walking is cheap. It can be done almost anywhere. Al
The difference in physical activity for the two groups is larger than the difference that could be expected to happen by chance alone.
You want to know the opinions of American high school teachers on the issue of establishing a national proficiency test as a prerequisite for graduation from high school. You obtain a list of all high school teachers belonging to the National Education As
The results of this survey may be affected by undercoverage and nonresponse.
Elephants sometimes damage trees in Africa. It turns out that elephants dislike bees. They recognize beehives in areas where they are common and avoid them. Can this information be used to keep elephants away from trees? Researchers want to design an expe
a) acacia trees
b) This allows the researchers to measure the effect of active hives and empty hives on tree damage compared to no hives at all.
c) Assign the trees numbered from 01 to 72 and use a random umber table to pick 24 different two-digit numbers
Google and Gallup teamed up to survey a random sample of 1673 US students in grades 7-12. One of the questions was "How confident are you that you could learn computer science if you wanted to?" Overall, 54% of students said they were confident.
a) Identi
a) population: all US students in grades 7-12; samples: The 1673 US students in grades 7-12 surveyed
b) Random selection reduces the effects of bias due to self-selection and also allows the results to be inferred to a larger population. In this case, stu
Many people start their day with a jolt of caffeine from coffee or a soft drink. Most experts agree that people who consume large amounts of caffeine each day may suffer from physical withdrawal symptoms if they stop ingesting their usual amounts of caffe
explanatory: The treatment given (caffeine capsule or placebo); Response: The time it takes to complete the tapping task.
b) Each of the 11 individuals will be a block in a matched pairs design. Each participant will take the caffeine tablets on one of th