Statistics: Mean and Standard Deviation Quiz

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Questions and Answers

What does the mean of a binomial distribution represent?

  • The sum of the probabilities of all outcomes
  • The total number of fixed trials
  • The maximum potential outcome of the distribution
  • The value you would expect after an infinite number of trials (correct)

If the number of fixed trials in a binomial distribution is 10 and the probability of success is 0.5, what is the mean (µ)?

  • 10
  • 15
  • 2
  • 5 (correct)

For a binomial distribution, what is the formula to calculate the standard deviation?

  • σ = Σ[x P(x)]
  • σ = sqrt(npq) (correct)
  • σ = µ + 2σ
  • σ = np

What indicates that a value is unusual according to the range rule of thumb?

<p>It lies outside the limits of µ + 2σ or µ – 2σ (C)</p> Signup and view all the answers

In a binomial distribution where the probability of success is 0.3 and there are 20 trials, what is the value of q?

<p>0.7 (B)</p> Signup and view all the answers

Given that p = 0.4 and n = 15, what is the variance (σ²) of the binomial distribution?

<p>7.2 (D)</p> Signup and view all the answers

If you are conducting a binomial experiment with 40 trials and a success rate of 0.25, what is the expected number of successes?

<p>10 (B)</p> Signup and view all the answers

If a binomial distribution has a mean of 8 and a standard deviation of 2, what is the minimum usual value?

<p>4 (A)</p> Signup and view all the answers

What would be a typical mean for the number of green M&Ms in a sample of 100 if the claimed rate is 16%?

<p>16 (A)</p> Signup and view all the answers

If a nursing student guesses on an exam with 75 true/false questions, what is the expected standard deviation for the number of correct answers?

<p>4.7 (A)</p> Signup and view all the answers

Is it unusual for a student to score at least 45 correct answers by guessing on the exam?

<p>No, it's expected. (C)</p> Signup and view all the answers

Based on the Experience.com poll, what is the total number of graduates who actually stayed at their first job less than 2 years?

<p>250 (A)</p> Signup and view all the answers

What range of usual values is calculated for the number of graduates who stay at their first job less than 2 years?

<p>(142.11, 177.89) (D)</p> Signup and view all the answers

What statistical methods were discussed for analyzing random samples from a population?

<p>Mean, variance and standard deviation (D)</p> Signup and view all the answers

If the claimed rate of graduates who stay less than 2 years is 50%, what is the standard deviation, assuming a sample size of 320?

<p>8.0 (C)</p> Signup and view all the answers

What conclusion can be drawn about the headline stating that 'most stay at first jobs less than 2 years' based on the results?

<p>It is unjustified because the actual number is too high. (B)</p> Signup and view all the answers

What parameter predominantly influences the Poisson distribution?

<p>Mean μ (A)</p> Signup and view all the answers

In which situation is the Poisson distribution typically used to approximate the binomial distribution?

<p>When n is large and p is small. (A)</p> Signup and view all the answers

How is the mean (μ) calculated in the context of the Poisson distribution?

<p>μ = np (D)</p> Signup and view all the answers

What is the probability of observing exactly one occurrence in the Poisson distribution if μ = 0.365?

<p>0.2534 (D)</p> Signup and view all the answers

In a Poisson process, what does the parameter μ represent?

<p>The average rate of occurrences (D)</p> Signup and view all the answers

Which of the following is a requirement for using the Poisson distribution to approximate the binomial distribution?

<p>n &gt;= 100, np &lt;= 10 (D)</p> Signup and view all the answers

Which scenario best illustrates a real-world application of the Poisson distribution?

<p>The number of emails received in an hour. (C)</p> Signup and view all the answers

When computing the probability that three or more parts will fail in ten years under certain conditions, which distribution is appropriate?

<p>Poisson distribution (A)</p> Signup and view all the answers

Which characteristic is NOT a requirement for a Poisson probability distribution?

<p>The interval must always be in units of time. (C)</p> Signup and view all the answers

When was the Poisson distribution first derived, and by whom?

<p>1837 by Siméon Poisson (B)</p> Signup and view all the answers

Which of the following is a suitable application of the Poisson distribution?

<p>The number of car accidents in a city in one year. (D)</p> Signup and view all the answers

What is required about the occurrences in a Poisson distribution?

<p>They must be uniformly distributed over the interval. (D)</p> Signup and view all the answers

Which of the following scenarios best illustrates a Poisson process?

<p>The number of orders at a restaurant during lunch. (C)</p> Signup and view all the answers

In the context of the Poisson distribution, what does the variable 'e' represent?

<p>The base of the natural logarithm, approximately 2.71828. (A)</p> Signup and view all the answers

What is the probability of an event occurring 'x' times over a specific interval in a Poisson distribution?

<p>Based on a formula involving 'e' raised to the power of negative mean. (C)</p> Signup and view all the answers

Which of the following events is considered a rare occurrence suitable for Poisson distribution analysis?

<p>The number of customer complaints at a bank per month. (A)</p> Signup and view all the answers

Which of the following scenarios would likely be modeled by a Poisson distribution?

<p>The number of car accidents on a road in a year (D)</p> Signup and view all the answers

What is characteristic of a Poisson distribution in terms of the mean and variance?

<p>Mean is equal to variance (A)</p> Signup and view all the answers

How would you determine the probability of a specific number of events occurring in an interval using a Poisson formula?

<p>By calculating the mean and using the Poisson probability formula (D)</p> Signup and view all the answers

Which of these examples is NOT well modeled by a Poisson distribution?

<p>Number of heads in 10 coin flips (B)</p> Signup and view all the answers

Which of the following statements about the Poisson distribution is true?

<p>It can be used for events that occur continuously over time (A)</p> Signup and view all the answers

In a Poisson distribution, if the average rate of occurrences is 4 events per hour, what is the expected probability of observing exactly 2 events in a 30-minute interval?

<p>0.1975 (D)</p> Signup and view all the answers

When considering the scenarios provided, which of the following can be most accurately modeled using a Poisson distribution?

<p>Number of cars passing a toll booth in an hour (C)</p> Signup and view all the answers

Flashcards

Binomial Probability Distribution Mean

The average number of successes in a fixed number of independent trials, where each trial has the same probability of success.

Binomial Probability Distribution Variance

Measures the spread or variability of the distribution of successes.

Binomial Probability Distribution Standard Deviation

The square root of the variance, providing a measure of the typical distance of observed values from the mean.

Expected Value

The average outcome of an experiment after a large number of repetitions.

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Range Rule of Thumb

A rough estimate of the range of usual values for a probability distribution.

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Minimum usual value

The lowest value considered likely to occur in a data set.

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Maximum usual value

The highest value considered likely to occur in a data set.

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n

Number of trials in a binomial experiment

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p

Probability of success in a single trial

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q

Probability of failure in a single trial. q = 1 - p

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Mean of Binomial Distribution

The expected value of the number of successes in a binomial experiment, calculated as n * p, where n is the number of trials and p is the probability of success in each trial.

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Standard Deviation of Binomial Distribution

The measure of the spread of the number of successes in a binomial experiment, calculated as the square root of n * p * (1 - p).

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Unusual Result in Binomial Experiment

A result that falls outside the typical range of outcomes, considered unlikely if the assumed probability is accurate.

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Range of Usual Values

The interval containing most of the expected values in a distribution, usually within plus or minus two standard deviations from the mean.

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Binomial Probability Distribution

A probability distribution that describes the probability of getting a certain number of successes in a fixed number of independent trials, where each trial has the same probability of success.

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Number of Successes in a Group

The count of favorable outcomes (successes) within a specific number of trials or within a sample group.

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Sample Size

The total number of observations or items in a sample.

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Probability of Success (p)

The likelihood of a specific outcome (success) in a single trial.

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Normal Distribution

A probability distribution that is symmetrical and bell-shaped. Many natural phenomena follow this pattern.

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16% rate

A stated probability or percentage (16%) of an event occurring

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Poisson Distribution

A discrete probability distribution that describes the probability of a given number of events occurring in a fixed interval of time or space, if these events occur with a known average rate and independently of the time since the last event.

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Requirements for Poisson Distribution

The random variable must count occurrences of an event over a specific interval. Occurrences must be random, independent, and uniformly distributed over the interval.

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Rare Events

Events that don't happen very often, but can still be predicted probabilistically with Poisson

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Poisson Formula

A mathematical formula used to calculate the probability of a given number of events occurring within a fixed interval. It involves the average rate of events (λ) and the factorial function.

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Interval (Poisson)

The specific period of time, area, or space in which the occurrence of events is being measured.

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Examples of Poisson Events

The number of customers arriving at a store in an hour, the number of misprints in a book, counts of radio-active decays.

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Poisson Distribution

A probability distribution that models the probability of a given number of events occurring in a fixed interval of time or space, if these events occur with a known average rate and independently of the time since the last event.

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Binomial Distribution

A probability distribution that describes the probability of getting a specific number of successes in a fixed number of independent trials, where each trial has the same probability of success.

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Poisson Approximation

Using the Poisson distribution to estimate probabilities from a binomial distribution when the number of trials (n) is large and the probability of success (p) is small.

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Rule of Thumb (Poisson Approximation)

Conditions for using the Poisson distribution as an approximation to the binomial: n ≥ 100 and np ≤ 10, where n is the number of trials and p is the probability of success.

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Parameter μ

The mean of the Poisson distribution, often calculated as np (product of number of trials and probability of success).

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Probability of "x" events

Specifies the chance of a particular number of events (x) occurring within a given interval, calculated using the Poisson distribution formula.

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Poisson Distribution

A probability distribution that models the number of events occurring in a fixed interval of time or space, where these events occur independently and at a constant average rate.

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Poisson Parameter (μ)

The average number of events expected in the specified interval.

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Number of Occurrences (x)

The actual count of events in a given interval.

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When is Poisson distribution suitable?

A Poisson distribution is appropriate when modeling events that occur independently and at a constant average rate, within a specified interval of time or space.

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Heart Attacks (Poisson)

Number of heart attacks in a specific region over a year, assuming independence between individuals.

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Plane Arrivals (Not Poisson)

Number of plane landings at an airport in a specific time interval, but likely not independent due to scheduling and traffic.

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Car Punctures (Possibly Poisson)

Number of car punctures on a highway over a year, although there could be factors leading to non-independence.

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Flooded Homes (Not Poisson)

Number of homes flooded in a region in a specific time period, likely not independent because floods affect multiple homes.

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Poisson Probability

Calculating the likelihood of a specific number of events occurring in a given time frame, given the average rate.

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Study Notes

Section 5.4: Mean and Standard Deviation of Binomial Probability Distributions

  • Binomial distributions involve important characteristics like center, variation, and distribution.
  • Given a binomial distribution, you can calculate its mean, variance, and standard deviation.
  • Emphasis is placed on interpreting these values.

Formulas for any Discrete Probability Distribution

  • Mean (μ): μ = Σ [x • P(x)]
  • Variance (σ²): σ² = Σ [x² • P(x)] – μ²
  • Standard Deviation (σ): σ = √[Σ x² • P(x)] – μ²

Formulas for Binomial Distributions

  • Mean (μ): μ = np

  • Standard Deviation (σ): σ = √(npq)

  • n = number of fixed trials

  • p = probability of success in one trial

  • q = probability of failure in one trial

Range Rule of Thumb

  • 95% of data lies within 2 standard deviations of the mean.
  • [μ – 2σ, μ + 2σ]
  • Values outside this range are considered unusual.

Example 1

  • Probability of a pea having a green pod is 0.75.
  • Expected number of green peas in 5 offspring: μ = np = 5(0.75) = 3.75

Example 2

  • Michael tested a theory that 75% of peas have green pods.
  • Collected 580 offspring; 428 had green pods.
  • Calculation shows this result is usual, not unusual.

Example 3

  • Mars Inc. claims 24% of its M&Ms are blue.
  • Independent researcher collected 100 M&Ms.
  • Expected mean and standard deviation for a sample of 100 M&Ms are calculated.
  • Finding the number of blue M&Ms that would be unusual, given the claim.

Example 4

  • Drug designed to increase the probability of a baby boy.
  • Monitored births of 152 babies.
  • 127 were boys.
  • The example shows that this result is unusual.

Other Examples

  • SAT multiple choice questions, random guessing.
  • A headline in USA Today about job tenure, based on Experience.com poll of 320 college graduates.

Recap

  • Mean, variance and standard deviation formulas for any discrete probability distribution.
  • Mean, variance and standard deviation formulas for the binomial probability distribution.
  • Interpreting results.

Homework

  • Pg. 232: 11, 13, 16, 18

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