Chap. 12

Question 1

Observational study

Answer 1

study based on data in which no manipulation of factors has been employed

Question 2

Retrospective study

Answer 2

an observational study in which subjects are selected and their previous behaviors or conditions are determined. need not to be based on random sampling and are usually an estimate of differences between groups and associations

Question 3

Prospective study

Answer 3

an observational study in which subjects are followed to observe future outcomes. focus on estimating differences among groups that might appear over the course of the study

Question 4

What makes something an experiment?

Answer 4

if treatments are deliberately being applied to subjects

Question 5

Experiment

Answer 5

manipulates factor levels to create treatments, randomly assigns subjects to those treatment levels, and compares the responses of subject groups across level treatments

Question 6

Random assignment

Answer 6

an experiment must assign experimental units to treatment groups at random in order to be valid

Question 7

Factor

Answer 7

variable whose levels are manipulated by the experiment, differences that factor levels may have on the response variable is what experiments discover (explanatory variable - how much sleep a third grader is or isn’t getting)

Question 8

Response variable

Answer 8

variable whose values are compared across different treatments, large response differences can be attributed to the effect of differences in treatment level

Question 9

Experimental units

Answer 9

individuals on whom an experiment is performed, usually called subjects or participants when they are human

Question 10

Level

Answer 10

specific values that the experimenter chooses for a factor are called the levels of the factor ( a third grader gets either 4,6, 8 hours of sleep)

Question 11

Treatment

Answer 11

process, intervention, or other controlled circumstance applied to randomly assigned experimental units, different levels of a single factor or are made up of combinations of levels of two or more factors

Question 12

1st Principal of design - control

Answer 12

aspects of the experiment that we know may have an effect on the response, but that aren’t the factors being studied

Question 13

2nd Principal of design - randomize

Answer 13

subjects to treatment to even out the effects that we cannot control

Question 14

3rd Principal of design - replicate

Answer 14

over as many subjects as possible - results for a single subject are just anecdotes. If the sample size is not representative, you have to repeat the experiment on a different group of subjects from a different part of the population

Question 15

4th Principal of design - blocking

Answer 15

to reduce the effects of identifiable attributes of the subjects that may affect their responses but can not be controlled

Question 16

Completely randomized design

Answer 16

all experimental units have an equal chance of receiving any treatment

Question 17

Statistically significant

Answer 17

when an observed difference is too large to believe it could have happened by chance

Question 18

Control group

Answer 18

experimental units assigned to a baseline treatment level, usually that’s either null or placebo - provide a basis of comparison

Question 19

Blinding

Answer 19

any individual associated with an experiment who is not aware of how subjects have been allocated to treatment groups

Question 20

Single-blind

Answer 20

when either those who can influence results or those who can evaluate the results is blinded

Question 21

Double-blind

Answer 21

when both those who can influence and those who can evaluate results are blinded

Question 22

Placebo

Answer 22

treatment known to have no effect, administered to one group so that all groups experience the same conditions because many response to a placebo we can observe weather a treatments affects is not simply due to placebo

Question 23

Placebo effect

Answer 23

tendency of many human subjects to show a response even when administering a placebo

Question 24

Blocking

Answer 24

when subgroups of experimental units differ in ways that may affect their responses to treatments, it is a good idea to gather them into blocks to isolate variability attributable to the differences between the blocks so that we can see the differences caused by the treatments more easily

Question 25

Randomized block design

Answer 25

subjects are randomly assigned to treatments only within blocks

Question 26

Matching

Answer 26

observational study where subjects who are similar in ways not under study may be matched and then compared with each other on the variables of interest which reduces unwanted variation

Question 27

Confounding

Answer 27

when the levels of one factor are associated with the levels of another factor in such a way that their effects cannot be separated