Lecture 10 - Designing Experiments, Blocking/Replication/Randomization, Causation, Sampling

Question 1

Which of the following best distinguishes an experimental study from an observational study?

A) Unlike observational studies, experimental studies must be run by statisticians.
B) In an experimental study, the investigator assigns some treatment to units involved in the study to observe the response.
C) An experimental study requires more people in the study compared to an observational study.
D) All of the above

Answer 1

B) In an experimental study, the investigator assigns some treatment to units involved in the study to observe the response.

Question 2

Which of the following is an observational study?

A) Researchers study the smoking habits of a group of patients in a hospital and record the incidence of lung cancer.
B) Doctors measure the temperature of patients in the ICU to see if the risk of sepsis increases with the increase in temperature.
C) Researchers record the eating habits of children over time to study the association between their diet and height.
D) All of the above

Answer 2

D) All of the above

Question 3

Principles of Experimental Design

Example: Sleep and Grades

Answer 3

We know that age and IQ are controlled. This means that changes in quiz grade with respect to sleep cannot be due to age or IQ.

Question 4

Blocking

Answer 4

• We want the only difference between the pair to be the treatment. Thus, if
  the response changes, we can say it’s due to the treatment

Question 5

Replication

Answer 5

• There could be extra variables we did not control for when we blocked.
• By replicating and randomizing, we can spread out confounding or lurking variables between the different treatment groups.

Question 6

Randomization

Answer 6

• There could be extra variables we did not control for when we blocked.
• By replicating and randomizing, we can spread out confounding or lurking
  variables between the different treatment groups.

Question 7

Un-Randomized Situation

Answer 7

Question 8

Randomized Situation

Answer 8

Question 9

Purpose?

Answer 9

Question 10

Activity: Read the following scenario and answer the questions

Answer 10

Question 11

Question

In this study, the unimpaired vision group is a:

A) Confounder
B) Control
C) Block
D) Match
E) None of the above

Answer 11

B) Control

Question 12

Question

In this study, the amount of prior driving experience is a:

A) Confounder
B) Control
C) Block
D) Match
E) None of the above

Answer 12

A) Confounder

Question 13

Causation AND
Observational Studies

Answer 13

Question 14

Activity: Design the following experiment.

Answer 14

Question 15

Causation AND
Experimental Studies

Answer 15

Question 16

Samples

Population vs Sample

Answer 16

Question 17

Statistical Inference

The procedure by which we reach a conclusion about a population based on the information contained in a sample that has been drawn from that population

Answer 17

• To produce precise inference, a sample needs to be as representative
  as possible of the population of interest
• If the sample is not a good representation of the population, sample error may occur making the statistical inferences invalid

Question 18

Sampling Designs/Methods

Non-Probability Sampling

Answer 18

Question 19

Sampling Designs/Methods

Probability Sampling

Answer 19

Question 20

Sampling Designs/Methods

Simple Random Sampling (SRS)

Answer 20

size 𝑛 consists of 𝑛 individuals from the population chosen in such a way that every set of 𝑛 individuals has an equal chance to be the sample actually selected

Question 21

Example

Simple Random Sampling (SRS)

Answer 21

• Picture a large amount of poker chips in a bowl with information written on each one.
• Reach in and randomly select 𝑛 chips.
• This represents our SRS.
• In practice, we sample without replacement (once a chip is selected, it’s not returned to the bowl).

Question 22

Answer 22