Descriptive Statistics Overview

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Questions and Answers

If event A is a subset of event B, which of the following is true?

  • A and B have no common outcomes.
  • Every outcome in B is in A.
  • Every outcome in A is in B. (correct)
  • The probability of A is greater than the probability of B.

The intersection of two disjoint events is always an empty set.

True (A)

What is the probability of an impossible event?

0

The complement of an event A consists of all outcomes in the sample space that are ______ in A.

<p>not</p> Signup and view all the answers

Match the set notations with their descriptions:

<p>$A \cup B$ = The outcomes that belong to A or B $A \cap B$ = The outcomes that belong to both A and B $A^c$ = The outcomes not in A $A \subseteq B$ = Every outcome in A is in B</p> Signup and view all the answers

Given a sample space of a fair six-sided die, what is the probability of rolling an even number?

<p>$1/2$ (C)</p> Signup and view all the answers

The probability of the union of two events is always equal to the sum of their individual probabilities.

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

Using the formula for the probability of a union of two events with the formula $P(A \cup B) = P(A) + P(B) - P(A \cap B)$, if $P(A) = 0.45$, $P(B) = 0.35$, and $P(A \cap B) = 0.1$, what is the value of $P(A \cup B)$?

<p>0.7</p> Signup and view all the answers

Which of the following is NOT a measure of central tendency?

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

The arithmetic mean is not affected by extreme values.

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

What property of the arithmetic mean makes it easy to calculate for any sample?

<p>simplicity</p> Signup and view all the answers

Measures of central tendency describe where the data are ______.

<p>located</p> Signup and view all the answers

Given the numbers 2, 4, 6, 8, and 10, what is the arithmetic mean?

<p>6 (C)</p> Signup and view all the answers

A student has test scores of 75, 80, and 90. What score does the student need on the next test to achieve an average of 85?

<p>95 (C)</p> Signup and view all the answers

Match the following terms with their descriptions:

<p>Arithmetic mean = The sum of all values divided by the number of values Median = The middle value of a sorted data set Mode = The value that appears most frequently in a data set</p> Signup and view all the answers

For a given set of data, there can be multiple arithmetic means.

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

What does IQR stand for?

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

The coefficient of variation is a unit-dependent measure.

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

In a box of 100 transistors, 20 are defective. If event A is selecting a defective transistor, what is P(A)?

<p>0.2 (D)</p> Signup and view all the answers

If the first quartile (Q1) is 10 and the third quartile (Q3) is 25, what is the interquartile range (IQR)?

<p>15</p> Signup and view all the answers

If events A and B are independent, then P(A ∩ B) = P(A) + P(B).

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

The interpercentile range (IPR) is the difference between two _________.

<p>percentiles</p> Signup and view all the answers

Given P(A ∩ B) = 15/100 and P(B) = 60/100, what is P(A|B)?

<p>0.25</p> Signup and view all the answers

In a dataset, if the position of Q3 is calculated to be 5.25, what value is typically used to find Q3?

<p>The value at position 6 (D)</p> Signup and view all the answers

Name two of the three counting techniques used to determine the number of outcomes of an experiment.

<p>Product rule, Permutations</p> Signup and view all the answers

If P(A) = 1/3 and P(B) = 1/2 and A and B are independent, then P(A∩B) is ______.

<p>1/6</p> Signup and view all the answers

In the transistor example, given that P(A ∩ B) = 15/100 and P(A) = 20/100, what is P(B|A)?

<p>0.75 (A)</p> Signup and view all the answers

Given a dataset, which of the following indicates greater dispersion?

<p>Higher Coefficient of Variation (CV) (A)</p> Signup and view all the answers

Match the following concepts with their appropriate formula:

<p>Interquartile Range (IQR) = 𝑄3 − 𝑄1 Coefficient of Variation (CV) = 𝑆/𝑋̄ × 100 Interpercentile range = 𝑃𝑛 − 𝑃𝑚</p> Signup and view all the answers

If the two events A and B are independent, then P(A|B) = P(A).

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

Match each probability notation to its correct definition:

<p>P(A) = Probability of event A occurring P(A|B) = Probability of event A occurring given that B has occurred P(A ∩ B) = Probability of both events A and B occurring P(B|A) = Probability of Event B occurring given that A has occurred</p> Signup and view all the answers

Which of the following statements is true regarding the t-distribution?

<p>It is bell-shaped and symmetric about t = 0. (D)</p> Signup and view all the answers

The shape of the t-distribution is independent of the sample size.

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

When using the t-distribution, what happens to its shape as the sample size increases?

<p>It gets closer to the standard normal distribution.</p> Signup and view all the answers

For a Chi-Square distribution, the curve is skewed to the ______.

<p>right</p> Signup and view all the answers

Match the following distributions with their key properties:

<p>t-distribution = Symmetric bell-shape; shape depends on sample size Chi-Square distribution = Skewed to the right Standard normal distribution = Approximated by the t-distribution with large sample sizes</p> Signup and view all the answers

Given a t-distribution, if $P(t \geq 2.571) = 0.025$, what is the probability $P(t < 2.571)$?

<p>0.975 (B)</p> Signup and view all the answers

If a sample of 4 cats is chosen at random from a population with an average weight of 12 pounds and a standard deviation of 8 pounds, and the sample average was found to be 7 pounds, what is the t-score calculated?

<p>-1</p> Signup and view all the answers

The chi-square distribution has degrees of freedom that are calculated based on the population mean.

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

Given events A and B, if $P(A) = 0.5$, $P(B) = 0.25$, and $P(A \cap B) = 0.2$, what is $P(A \cup B)$?

<p>0.55 (B)</p> Signup and view all the answers

If two events A and B are disjoint, then $P(A \cap B) = 1$.

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

If a fair die is rolled twice, how many possible outcomes are there?

<p>36</p> Signup and view all the answers

If $P(A) = 0.7$, then $P(A^\prime) = $ ______.

<p>0.3</p> Signup and view all the answers

Match the following probabilities with their meanings given $P(A) = 0.6$, $P(B) = 0.3$ and $P(A \cap B) = 0.1$.

<p>$P(A \cup B)$ = 0.8 $1 - P(A)$ = 0.4 $P(A|B)$ = 1/3 $1 - P(A \cap B)$ = 0.9</p> Signup and view all the answers

If $P(A) = 0.5$, $P(B) = 0.25$ and $P(A \cap B) = 0.2$, what is $P(A^\prime \cup B^\prime)$?

<p>0.8 (D)</p> Signup and view all the answers

If events A and B are not disjoint, then $P(A \cap B)$ must be greater than zero.

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

A balanced coin is tossed 5 times. How many possible outcomes are there?

<p>32</p> Signup and view all the answers

The formula for conditional probability $P(A|B)$ is $P(A \cap B) / $ ______.

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

Given two events A and B with $P(A|B) = 0.4$ and $P(A \cap B) = 0.2$, what is $P(B)$?

<p>0.5 (B)</p> Signup and view all the answers

Flashcards

Measures of Central Tendency

A statistical measure that describes the central or typical value of a dataset. It indicates where the majority of the data points are clustered.

Arithmetic Mean

The sum of all values in a dataset divided by the total number of values. It is the most commonly used measure of central tendency.

Median

The middle value in a sorted dataset. It divides the data into two equal halves, where half the values are greater than the median and half are less.

Mode

The value that appears most frequently in a dataset. It is the most common value in the set.

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Sample Space (Ω)

The set of all possible outcomes of a random experiment.

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Event (A)

A set of outcomes from a sample space.

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Complement of an event (Ā)

The set of outcomes in the sample space that are not in the event.

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Event A is a subset of Event B

All outcomes in A are also in B.

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Intersection of Events (A ∩ B)

The outcomes that belong to both events A and B.

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Union of Events (A ∪ B)

The outcomes that belong to either event A or event B.

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Disjoint Events (A and B)

Events A and B have no outcomes in common. A ∩ B = ∅

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Classical Probability

The probability of an event is the number of favorable outcomes divided by the total number of outcomes.

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Interquartile Range (IQR)

The difference between the third quartile (Q3) and the first quartile (Q1). It measures the spread of the middle 50% of the data.

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Coefficient of Variation (CV)

Used to compare the dispersion of data sets with different means and units, it's the ratio of the standard deviation to the mean.

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Product Rule

A technique used to determine the number of possible outcomes in an experiment where each step has a fixed number of choices. You multiply the number of choices at each step to find the total number of outcomes.

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Permutation

A way to calculate the number of ways to arrange a specific number of items from a set, where order matters.

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Third Quartile (Q3)

The value that separates the top 25% of the data from the bottom 75%. It is the 75th percentile.

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First Quartile (Q1)

The value that separates the top 75% of the data from the bottom 25%. It is the 25th percentile.

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Interpercentile Range (IPR)

The difference between two percentiles in a data set. It describes the spread of the data between those two percentiles.

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Percentile Position

The position of a percentile in a data set. It is calculated by multiplying the desired percentile by the total number of observations and dividing by 100.

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t-distribution

A statistical distribution used to estimate population parameters, such as the mean or variance, when the population standard deviation is unknown and the sample size is small.

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Degrees of Freedom (d.f.) for t-distribution

The number of independent pieces of information that are used to estimate a parameter. For the t-distribution, the degrees of freedom are calculated as (n-1), where n is the sample size.

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t-test

A statistical test used to determine whether there is a significant difference between the means of two populations or between the mean of a population and a specific value.

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Chi-square distribution

A statistical distribution used to test the hypothesis that the variance of a population is equal to a specific value. It uses the sample variance to estimate the population variance.

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Chi-square test

A statistical test that compares the observed frequencies of categories to the expected frequencies, based on the null hypothesis that there is no association between the categories.

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Degrees of Freedom (d.f.) for Chi-square Distribution

The shape of the chi-square distribution depends on the degrees of freedom, which is calculated as one less than the number of categories (n-1).

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P-value

The probability of getting a test statistic as extreme or more extreme than the observed value, assuming the null hypothesis is true.

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Confidence Level

Confidence level is the probability that the true population parameter lies within the confidence interval.

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Conditional Probability (P(A|B))

The probability of event A occurring given that event B has already occurred.

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Disjoint Events

Two events are disjoint if they cannot happen at the same time. Their intersection is empty.

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Joint Probability (P(A∩B))

The probability of the intersection of two events A and B, or the probability of both A and B happening.

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Union Probability (P(A∪B))

The probability of the union of two events A and B, or the probability of either A or B happening (or both).

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Complement Probability (P(A̅))

The probability of event A not happening, calculated by 1 minus the probability of A.

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Calculating Total Outcomes

The number of possible outcomes of a random experiment where there are 'n' trials and 'k' outcomes in each trial, for example.

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Conditional Probability Formula

The probability of an event A occurring given that event B has already occurred. It's calculated as the probability of both A and B happening divided by the probability of B.

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Independent Events

Two events are independent if the occurrence of one event does not affect the probability of the other event occurring.

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Probability Value Range

The probability of an event is a value between 0 and 1, where 0 indicates impossibility and 1 indicates certainty.

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Calculating Probability

The probability of an event can be determined by dividing the number of favorable outcomes by the total number of possible outcomes.

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Marginal Probability (P(A))

The probability of an event occurring given no prior information about other events influencing it. It is simply the number of favorable outcomes divided by the total number of outcomes.

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Probability of Neither Event Occurring (P(A' ∩ B'))

The probability of both events A and B not occurring. It is calculated by subtracting the probability of either event occurring (P(A) + P(B) - P(A ∩ B)) from 1.

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Study Notes

Descriptive Statistical Measures

  • Measures of central tendency describe the location of data.
  • Common measures include arithmetic mean, median, and mode.

Arithmetic Mean

  • The sample mean (average) is calculated by summing all data points and dividing by the total number of data points.
  • Formula: X = (X₁ + X₂ + ... + Xₙ) / n

Examples of Arithmetic Mean Calculations

  • The mean of 9, 3, 7, 3, 8, 10, 2 is 6
  • The average of 96, 94, 72, 52, 56 marks is 74

Properties of Arithmetic Mean

  • A unique mean exists for a given dataset
  • Easy to calculate
  • Affected by extreme values, making it potentially not entirely representative of the majority of data

Median

  • The median is the middle value in a sorted dataset.
  • In an odd-sized dataset, the median is the middle value.
  • In an even-sized dataset, the median is the average of the two middle values.

Mode

  • The mode is the most frequently occurring value in a dataset.
  • A dataset can have multiple modes or no mode.

Measures of Variation (Dispersion)

  • Dispersion statistics summarize the spread or scatter of data.
  • Common measures of dispersion include range, variance, standard deviation, interquartile range, and interpercentile range.

Range

  • Range = maximum observation – minimum observation

Examples of Range Calculations

  • Range of 13, 18, 13, 14, 16, 14, 21, 13 is 8
  • If Jordan's hottest temperature was 39.2° and range is 40.7°, the coldest temp is -1.5°

Variance

  • Formula for sample variance S2 = Σᵢ=₁ (xᵢ-X)² / (n-1) Where: xᵢ = each data point X = sample mean n = total number of values

Standard Deviation

  • Standard deviation is the square root of the variance.
  • Formula: √S² = s

Quartiles, Deciles, and Percentiles

  • Quartiles divide data into four equal parts.
  • First quartile (Q1) is the 25th percentile.
  • Second quartile (Q2) is the 50th percentile, which is the median.
  • Third quartile (Q3) is the 75th percentile.
  • Deciles divide data into 10 equal parts.
  • Percentiles divide data into 100 equal parts.

Interquartile Range (IQR)

  • IQR = Q3 − Q1

Interpercentile Range (IPR)

  • IPR = pₙ − pₘ Where pₙ and pₘ represent the nth and mth percentile, respectively

Coefficient of Variation (CV)

  • Formula: CV = (s / x̄) * 100 Where s = sample standard deviation and x̄ = sample mean

Counting Techniques

  • Product rule: The total number of ways to complete a sequence of steps is the product of the number of ways to complete each step if the choice of each step is not conditional upon previous steps.
  • Permutations: An arrangement of objects where order matters without repetition
  • Combinations: An arrangement of objects where order does not matter without repetition

Factorials

  • n! (n factorial) is the product of all positive integers less than or equal to n.
  • 0! = 1

Sample Space and Events

  • Sample space (Ω) is the set of all possible outcomes of a random experiment.
  • An event is a subset of the sample space.
  • Empty set (Ø) and the sample space (Ω) are considered events.

Conditional Probability

  • The probability of event A given event B is P(A|B) = P(A ∩ B) / P(B) P(A|B) = Probability of event A occurring given event B occurred

Independent Events

  • A and B are independent if and only if P(A ∩ B) = P(A)P(B)

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