Exam 2: Collecting Data Sensibly

A control group provides a baseline for comparison to a treatment group.

The ZZZ chain of motels has a standard method of constructing their rooms to maximize the ease of parking for its customers.The rooms are arranged in adjacent buildings so that each customer can park outside the rented room.The layout for one of the with 48 rooms located along a famous highway is diagrammed below:

Blocking is a technique that can be used to filter out the effects of extraneous factors.

Selection bias can occur if volunteers only are used in a study.

The two paragraphs below discuss aspects of two studies, each of which exhibit a bias.For each study, decide whether the problem is selection bias, response bias, or nonresponse bias, and in a few sentences explain why you chose your answer.

The most basic sampling method studied in statistics is the simple random sample (SRS).In your own words, what is the correct definition of a simple random sample of size n?

By definition, a simple random sample of size n is any sample that is selected in a manner to guarantee every individual in the population has an equal chance of selection.

If the subjects as well as the person measuring the response are aware of the treatment assigned to the subject, only single-blinding is being used.

Random subpopulations of a population are called strata.

The following paragraph describes an actual study.After reading the description, determine whether the study is an observational or experimental study.Justify your answer with specific references to the information in the study. "Before the opening of the new International Airport and the termination of the old airport, children near both sites were recruited into aircraft-noise groups (aircraft noise at present or pending)and control groups with no aircraft noise and closely matched for socio-economic status.A total of 326 children (mean age = 10.4 years)took part in three data-collection waves, one before and two after the switch-over of the airports.After the switch to the new airport, long- term memory and reading were found to be impaired in the noise group at the new airport, and improved in the formerly noise-exposed group at the old airport."

In a well-designed experiment, the factors are confounded whenever possible.

Increasing sample size will generally eliminate bias in a sample.

Clusters are non-overlapping subgroups of a population that have been identified as homogeneous.

A placebo is identical in appearance to the treatment of interest, but contains no active ingredients.

Stratified sampling is a sampling method that in no way involves simple random sampling.

A study is an observational study if the investigator observes the behavior of a response variable when one or more factors are manipulated.

Three methods for random sampling are: (a)simple random sampling, (b)stratified random sampling, and (c)cluster sampling.In a few sentences, discuss the similarities and differences among these sampling methods.Specifically, what sampling circumstances would lead you to choose each of these methods?

A friend of yours, who is not taking statistics, wonders why it is that anyone would choose to take a sample."Obviously," she says, "you would get better information from a census." In a short paragraph, explain why it is that statisticians take samples rather than taking a census.

Random assignment to treatments will guarantee groups that are exactly alike for experimental purposes.

Response bias can occur when responses are not actually obtained from all individuals selected for inclusion in the sample.