Chapter 4: Probability

Question 1

test sensitivity

Answer 1

The probability of a true positive, given that the subject actually has the condition being tested.

Question 2

test specificity

Answer 2

The probability of a true negative, given that the subject does not have the condition being tested.

Question 3

positive predictive value

Answer 3

Probability that a subject is a true positive, given that the test yields a positive result (indicating that the condition is present).

Question 4

negative predictive value

Answer 4

Probability that the subject is a true negative, given that the test yields a negative result (indicating that the condition is not present).

Question 5

prevalence

Answer 5

Proportion of subjects having some condition.

Question 6

rare event rule for inferential statistics

Answer 6

If, under a given assumption, the probability of a particular observed event is extremely small, we conclude that the assumption is probably not correct.

Question 7

event

Answer 7

Any collection of results or outcomes of a procedure.

Question 8

simple event

Answer 8

An outcome or an event that cannot be further broken down into simpler components.

Question 9

sample space

Answer 9

All possible simple events in a procedure; all outcomes that cannot be broken down any further.

Question 10

What does the notation “P” denote?

Answer 10

probability

Question 11

What do the notions “A,B, and C” denote?

Answer 11

specific events

Question 12

What does the notation “P(A)” denote?

Answer 12

the probability of event A occurring

Question 13

When using the classical approach to find the probability of an event, it is important to verify that the each simple event in the procedure are what?

Answer 13

equally likely to occur

Question 14

law of large numbers

Answer 14

As a procedure is repeated again and again, the relative frequency probability of an event tends to approach actual probability.

Question 15

How is relative frequency probability calculated?

Answer 15

number of times “A” occurred divided by the number of times the procedure was repeated

Question 16

Are the results of a relative frequency probability calculation exact values or approximations?

Answer 16

Approximations. A probability estimate based on only a few trials can be off by a substantial amount, but with a very large number of trials, the estimates tend to be more accurate.

Question 17

How is probability calculated using the classical approach?

Answer 17

The number of ways “A” occurred is divided by the number of different simple events.

Question 18

How are subjective probabilities determined?

Answer 18

The probability of event “A” is estimated by using knowledge of the relevant circumstances. In other words, you make an educated guess.

Question 19

When the occurrence of an event is impossible, what is its probability?

Answer 19

0

Question 20

When an event has a 50-50 chance of occurring, what is its probability?

Answer 20

0.5

Question 21

When an event is certain to occur, what is its probability?

Answer 21

1

Question 22

What is a complement of an event consist of?

Answer 22

All of the outcomes in which event “A” does NOT occur.

Question 23

Which is more likely to occur, an event with 0.00001 probability or an event with 0.15 probability?

Answer 23

An event with 0.15 probability.

Question 24

How often, on average, does an event with a probability of 0.001 occur?

Answer 24

Once in a thousand trials.

Question 25

An event is unlikely to occur if its probability is at or below what number?

Answer 25

0.05

Question 26

When does an event have an unusually low or unusually high number of outcomes?

Answer 26

When the number of outcomes is far from what is typically expected.

Question 27

actual odds against

Answer 27

The actual odds against event “A” occurring are the ration P(A-)/P(A), usually expressed in the form of a:B (or “a to b”, where “a” and “b” are integers having no common factors.

Question 28

actual odds in favor

Answer 28

The actual odds in favor of event “A” occurring are the ratio P(A)/P(A-), which is the reciprocal of the actual odds against that event. If the odds against “A” are a:b, then the odds in favor of “A” are b:a.

Question 29

payoff odds

Answer 29

The payoff odds against event A occurring are the ratio of net profit (if you win) to the mount bet:
payoff odds against event A= (net profit):(amount bet)

Question 30

false positive

Answer 30

WRONG result in which test incorrectly indicates the presence of a condition when the subject actually does not have that condition.

Question 31

false negative

Answer 31

WRONG result in which the test incorrectly indicates that the subject does NOT have a condition when it really is present.

Question 32

true positive

Answer 32

CORRECT result in which the test correctly indicates that a condition is present when it really is present.

Question 33

true negative

Answer 33

CORRECT result in which the test correctly indicates that a condition is not present when it really is not present.

Question 34

What is a simulation of a procedure?

Answer 34

A process that behaves in the same ways as the procedure itself so that similar results are produced.

Question 35

What is a compound event?

Answer 35

Any event combining 2 or more simple events.

Question 36

What is the intuitive addition rule for compound events?

Answer 36

To find P (A or B), find the sum of the number of ways event A can occur and the number of ways event B can occur, ADDING IN SUCH A WAY THAT EVERY OUTCOME IS COUNTED ONLY ONCE. P(A or B) is equal to that sum, divided by the total number of outcomes in the sample space.

Question 37

When are events A and B be considered to be “disjoint” (or mutually exclusive)?

Answer 37

When they cannot occur at the same time. (That is, disjoint events do not overlap)

Question 38

Whenever A and B are disjoint, what does P (A and B) become?

Answer 38

Zero.

Question 39

What is the formal addition rule for compound events?

Answer 39

P(A or B)= P(A)+ P(B)- P(A and B)