MODULE 2 - STUDY DESIGNS AND SAMPLING

Question 1

4 goals that all sampling designs must achieve

Answer 1

1. all sampling units are selectable
2. selection is unbiased
3. selection is independent
4. all samples are possible

Question 2

all sampling units are selectable explanation

Answer 2

This goal is about the sampling unit. Every sampling unit in the statistical population must have some non-zero probability of being included in your sample.

Question 3

selection is unbiased explanation

Answer 3

The probability of selecting a particular sampling unit cannot depend on any attribute of that sampling unit and—on average—the sampling units must have the same attributes as the statistical population.

Question 4

selection is independent explanation

Answer 4

Selection of a particular sampling unit must not increase or decrease the probability that any other sampling units is selected.

Question 5

all samples are possible explanation

Answer 5

This goal is about the sample composition. All samples that could be created from the statistical population are possible.

Question 6

With the aim of increasing the number of responses, a phone pollster decided to ask 2 people in each randomly selected house to answer a questionnaire. What type of error will this cause?

Answer 6

non-independence

Question 7

What goal does the following statement refer to? “every combination of units must be possible in your sample”

Answer 7

equal chances for all samples

Question 8

what is an observational study

Answer 8

a study using observations from a statistical population where the investigator has no control over the explanatory variables

Question 9

primary goal of an observational study

Answer 9

to characterize something about an existing statistical population

Question 10

problem with observational studies

Answer 10

provide a tool for discovering associations, but they cannot make statements about whether a factor causes the response you are interested in

Question 11

what is an explanatory variable?

Answer 11

a variable that an investigator believes may explain the response variable

Question 12

what is a confounding variable?

Answer 12

unobserved variables that affect a response variable

Question 13

5 designs for observation studies

Answer 13

1. simple random survey
2. stratified survey
3. cluster survey
4. case-control survey
5. cohort survey

Question 14

what is a simple random survey?

Answer 14

sampling units are selected at random from the statistical population

Question 15

what is a stratified survey?

Answer 15

sampling units are selected from within predefined groups

Question 16

what is a cluster survey?

Answer 16

groups of observation units are selected at random

Question 17

what is a case-control survey?

Answer 17

sampling units are selected based on the response variable

Question 18

what is a cohort survey?

Answer 18

sampling units are selected and then followed through time

Question 19

what is a retrospective study?

Answer 19

where the outcome is already known, which comes with an increased risk of spurious relationships if you are selecting groups based on the outcome

case-control studies are a good example of a retrospective study

Question 20

what is a prospective study?

Answer 20

where the outcome is not yet known

cohort studies are a good example of a prospective study

Question 21

what is a cross-sectional study?

Answer 21

that study a response variable at only a single snapshot in time

Question 22

what is a longitudinal study?

Answer 22

that study a response variable at multiple points in time

Question 23

what is an experimental study?

Answer 23

a study using involving a statistical population where the investigator can control the explanatory variables

Question 24

primary goal of an experimental study

Answer 24

to study the effect of one (or more) manipulated variables on one (or more) response variables

Question 25

what is a factor?

Answer 25

any manipulated variable in an experimental study

Question 26

what is a level?

Answer 26

the manipulated value within each factor

Question 27

2 key things that distinguish experimental studies from observational studies

Answer 27

1. the explanatory variable is manipulated by the researcher
2. sampling units are randomly assigned to each level in a factor

Question 28

what is replication?

Answer 28

the idea that a treatment will be repeated a number of times to see how repeatable a measured outcome is

the number of times a treatment is repeated on independent, representative and randomly selected units

Question 29

what is pseudoreplication?

Answer 29

an error in the design of an experimental study where the observation units are analyzed rather than the sampling units

Question 30

5 design elements of experimental studies

Answer 30

1. control treatment
2. blocking
3. blinded
4. placebo
5. sham treatment

Question 31

what is a control treatment?

Answer 31

is common in experimental studies and is intended as a reference treatment to compare against the treatment levels that alter the explanatory variable

It contains everything that the treatment levels do, except the treatment itself

Question 32

what is blocking?

Answer 32

is analogous to stratified sampling, but for experimental studies

It is used to control for variation among the sampling units that is not of interest to the researcher

Question 33

what is blinded?

Answer 33

commonly used in experimental studies involving people and refers to a design where the sampling unit (usually a person, but could be a group of people) does not know what treatment they are being exposed to

Question 34

what is a placebo?

Answer 34

a method often used in medical trials for the control treatment that helps accomplish a blinded design

It is substance, or treatment, that has no effect on the response variable

Question 35

what is a sham treatment?

Answer 35

similar to placebo in that it is a method used in control treatments

the purpose of a sham treatment
is slightly different in that it aims to account for the effect of delivery of a treatment that is not of interest to the researcher

Question 35

what is a sham treatment?

Answer 35

similar to placebo in that it is a method used in control treatments

the purpose of a sham treatment
is slightly different in that it aims to account for the effect of delivery of a treatment that is not of interest to the researcher

Question 36

Imagine a study that evaluates the effectiveness of different over-the-counter pain relievers in alleviating the symptoms of arthritis: acetaminophen, ibuprofen and acetylsalicylic acid. Two hundred patients are randomly assigned to receive one of these three pain relievers, or to receive a placebo (control). How many factors and levels are evident in this study?

Answer 36

1 factor with 4 levels

Question 37

Patients who are blinded to the experimental treatment is a crucial part of a randomized clinical trial. Why?

Answer 37

Reduces the possibility of placebo effects

Reduces biases in measurements stemming from the anticipation of a treatment effect

Question 38

A researcher studied the effect of the prescription drug raloxifene on fracture risk in postmenopausal women. They found that women who took raloxifene over a five year period reduced their risk of clinical vertebrate fracture compared to women who did not take the drug. What are the factors and levels in this experiment?

Answer 38

1 factor (drug) and 2 levels (raloxifene, no raloxifene)