OpenStax - Ch. 4 Discrete Random Variables

Question 1

Bernoulli Trials

Answer 1

an experiment with the following characteristics:

There are only two possible outcomes called “success” and “failure” for each trial.

The probability p of a success is the same for any trial (so the probability q = 1 − p of a failure is the same for any trial).

Question 2

Binomial Experiment

Answer 2

a statistical experiment that satisfies the following three conditions:

There are a fixed number of trials, n.

There are only two possible outcomes, called “success” and, “failure,” for each trial. The letter p denotes the probability of a success on one trial, and q denotes the probability of a failure on one trial.

The n trials are independent and are repeated using identical conditions.

Question 3

Binomial Probability Distribution

Answer 3

a discrete random variable (RV) that arises from Bernoulli trials; there are a fixed number, n, of independent trials. “Independent” means that the result of any trial (for example, trial one) does not affect the results of the following trials, and all trials are conducted under the same conditions. Under these circumstances the binomial RV X is defined as the number of successes in n trials. The notation is: X ~ B(n, p). The mean is μ = np and the standard deviation is σ = npq−−−√npq. The probability of exactly x successes in n trials is

Question 4

Expected Value

Answer 4

expected arithmetic average when an experiment is repeated many times; also called the mean. Notations: μ. For a discrete random variable (RV) with probability distribution function P(x),the definition can also be written in the form μ = ∑∑xP(x).

Question 5

Geometric Distribution

Answer 5

a discrete random variable (RV) that arises from the Bernoulli trials; the trials are repeated until the first success. The geometric variable X is defined as the number of trials until the first success.

Question 6

Geometric Experiment

Answer 6

a statistical experiment with the following properties:

1. There are one or more Bernoulli trials with all failures except the last one, which is a success.
2. In theory, the number of trials could go on forever. There must be at least one trial.
3. The probability, p, of a success and the probability, q, of a failure do not change from trial to trial.

Question 7

Hypergeometric Experiment

Answer 7

a statistical experiment with the following properties:

1. You take samples from two groups.
2. You are concerned with a group of interest, called the first group.
3. You sample without replacement from the combined groups.
4. Each pick is not independent, since sampling is without replacement.
5. You are not dealing with Bernoulli Trials.

Question 8

Hypergeometric Probability

Answer 8

a discrete random variable (RV) that is characterized by:

1. A fixed number of trials.
2. The probability of success is not the same from trial to trial.

We sample from two groups of items when we are interested in only one group. X is defined as the number of successes out of the total number of items chosen.

Notation: X ~ H(r, b, n), where r = the number of items in the group of interest, b = the number of items in the group not of interest, and n = the number of items chosen.

Question 9

Mean

Answer 9

a number that measures the central tendency; a common name for mean is ‘average.’ The term ‘mean’ is a shortened form of ‘arithmetic mean.’

Question 10

Mean of a Probability Distribution

Answer 10

the long-term average of many trials of a statistical experiment.

Question 11

Poisson Probability Distribution

Answer 11

a discrete random variable (RV) that counts the number of times a certain event will occur in a specific interval; characteristics of the variable:

• The probability that the event occurs in a given interval is the same for all intervals.
• The events occur with a known mean and independently of the time since the last event.

Question 12

Probability Distribution Function (PDF)

Answer 12

a mathematical description of a discrete random variable (RV), given either in the form of an equation (formula) or in the form of a table listing all the possible outcomes of an experiment and the probability associated with each outcome.

Question 13

Random Variable (RV)

Answer 13

a characteristic of interest in a population being studied; common notation for variables are upper case Latin letters X, Y, Z,…; common notation for a specific value from the domain (set of all possible values of a variable) are lower case Latin letters x, y, and z. For example, if X is the number of children in a family, then x represents a specific integer 0, 1, 2, 3,…. Variables in statistics differ from variables in intermediate algebra in the two following ways.

The domain of the random variable (RV) is not necessarily a numerical set; the domain may be expressed in words; for example, if X = hair color then the domain is {black, blond, gray, green, orange}.

We can tell what specific value x the random variable X takes only after performing the experiment.

Question 14

Standard Deviation of a Probability Distribution

Answer 14

a number that measures how far the outcomes of a statistical experiment are from the mean of the distribution

Question 15

The Law of Large Numbers

Answer 15

As the number of trials in a probability experiment increases, the difference between the theoretical probability of an event and the relative frequency probability approaches zero.