Types of Bias
when sampling methods either over or under emphasize some characteristic of the population
What is bias?
the process, intervention, etc that is applied to each subject in an experiment
What is treatment?
A restaurant leaves comment cards on all of its tables and encourages customers to participate in a brief survey to learn about their overall experience. What type of bias is this?
What is voluntary response bias?
sampling schemes that combine several different sampling methods at different stages
What is multistage sampling?
What prevents this study from being a well-designed experiment?
Thirty-six students at a local middle school were randomly selected to participate in a taste test to select a new menu item for a cafeteria. Each student was given a choice between the mac and cheese and the pancakes. From the sample, 20 students selected mac and cheese and 16 students chose pancakes. Each student was asked to rate the item they chose on a scale from 1 (extremely dislike) to 9 (extremely like).
Why were treatments (new menu items) not randomly assigned to the students?
bias where we allow members of our population to respond at will
What is voluntary response bias?
a fake treatment often given to the control group to help prevent the placebo effect
What is placebo?
A quality control worker at a factory selects the first items she sees as her sample for the day. What type of bias is this?
What is convienience sampling?
a sample is drawn from the population by following a systematic plan to give every object in the population an equal chance to be chosen but all possible groups can not be formed
what is systematic sampling?
when the subjects as well as those evaluating the result of an experiment do not know which subjects are in the treatment or control groups
What is double blind?
some portion of the intended population is either unrepresented or under-represented
What is undercoverage bias?
subjects or experimental units are grouped together homogeneously because of some characteristic they have in common that is believed might effect the experiment
What is blocking?
Each student at a school has a student identification number. Counselors have a computer generate random identification numbers and those students are asked to take a survey. What type of sampling method is this?
What is simple random sample?
population is split into diverse parts (usually based on geography) and then entire groups are selected randomly and sampled
What is cluster sampling?
A scientist studying soil acidity collected soil samples from a plot of land with a stream running through it. The soil samples came from land located on only one side of the stream. What is the type of bias is this?
What is undercoverage bias?
bias created when people who are randomly selected refuse to participate in the sample
What is nonresponse bias?
a group created to provide a basis for comparison usually either an old or placebo treatment
What is a control group?
A principal orders t-shirts and wants to check some of them to make sure they were printed properly. She randomly selects of the boxes of shirts and checks every shirt in those boxes. What type of sampling method is this?
What is cluster sampling?
population is divided into homogeneous groups and then a random sample is drawn from each group
What is stratified random sampling?
The president of a small company needs to collect data on the educational background of all 20 of the company’s employees. Which sampling method would work best?
What is a census?
anything in the survey design that influences the responses from the sample
What is response bias?
a variable whose levels are controlled by the experimenter to discover its effects on the subjects
What is a factor?
A school chooses randomly selected athletes from each of its sports teams to participate in a survey about athletics at the school. What type of sampling method is this?
What is stratified random sampling?
this requires that every item in the population has an equal chance to be chosen and that every possible combination of items has an equal chance to exist
What is simple random sample?
To estimate the size of a typical housing unit in a certain town, a sociologist plans to use a cluster sampling method to gather data. Which of the following describes a cluster sampling method?
What is dividing the town into nonoverlapping regions, randomly selecting regions, and selecting all housing units in those regions?