Chapter 3: Problem 46
Construct probability histograms for the binomial probability distributions for \(n=5\) \(p=.1, .5,\) and. \(9 .\) (Table \(1,\) Appendix 3 , will reduce the amount of calculation.) Notice the symmetry for \(p=.5\) and the direction of skewness for \(p=.\). 1and. \(.9 .\)
Short Answer
Expert verified
Histograms: \( p=0.1 \) right-skewed, \( p=0.5 \) symmetric, \( p=0.9 \) left-skewed.
Step by step solution
01
Understand the Binomial Distribution
A binomial distribution represents the probability of having exactly 'k' successes in 'n' independent Bernoulli trials, each with success probability 'p'. For this task, we repeat the trials 5 times (i.e., \( n = 5 \)) with three different probabilities (\( p = 0.1, 0.5, 0.9 \)).
02
Calculate Probabilities for p = 0.1
The probability mass function of a binomial distribution is given by: \[ P(X = k) = \binom{n}{k} p^k (1-p)^{n-k} \]For \( p = 0.1 \), the probabilities for \( k = 0, 1, 2, 3, 4, 5 \) can be calculated using this formula.
03
Calculate Probabilities for p = 0.5
Using the same formula, calculate the probabilities for each value of \( k \) when \( p = 0.5 \). This distribution should be symmetric around the mean, which is \( np = 2.5 \).
04
Calculate Probabilities for p = 0.9
Again, use the binomial formula to find probabilities when \( p = 0.9 \). In this case, more weight will be to the values at the higher end (around \( k = 5 \)), demonstrating a skew toward higher successes.
05
Construct the Histogram for p = 0.1
Plot the probabilities calculated for \( p = 0.1 \) on the y-axis and the number of successes (\( k \)) on the x-axis. The resulting histogram will be right-skewed, showing that fewer successes are more likely.
06
Construct the Histogram for p = 0.5
Plot the probabilities for \( p = 0.5 \) similarly. Here, you will observe a symmetric histogram centered around the mean, indicating equal likelihood of successes and failures.
07
Construct the Histogram for p = 0.9
Using the probabilities calculated for \( p = 0.9 \), plot the histogram with \( k \) on the x-axis. This histogram will be left-skewed, showing that more successes are quite likely.
08
Analyze the Symmetry and Skewness
Compare the histograms: notice symmetry around the center for \( p = 0.5 \) and skewness to the right for \( p = 0.1 \) and to the left for \( p = 0.9 \). This reflects how the probability of success affects the distribution shape.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Probability Histograms
A probability histogram provides a visual representation of a probability distribution. When dealing with a binomial distribution, a histogram allows us to see the probabilities of different numbers of successes in a series of trials. In our exercise, we are exploring how this visual representation changes based on different probabilities of success.
- For a binomial distribution with 5 trials and a success probability of 0.1, most of the probabilities will be concentrated at the lower end. This results in a histogram that shows a greater chance of 0 or 1 success, creating a skew towards the right.
- With a success probability of 0.5, the histogram is balanced. This means it's symmetric around the mean, which is calculated as the number of trials multiplied by the probability, \(np = 2.5\). As such, we get a bell-shaped histogram centered at 2 or 3 successes.
- Lastly, when the probability of success is high, say 0.9, the histogram shifts towards the higher number of successes, demonstrating a left skew. This is because there is a higher chance of achieving 4 or 5 successful trials.
Skewness
Skewness in a distribution describes the direction and the extent of asymmetry from a normal distribution. When dealing with a binomial distribution, skewness can tell us whether the probability mass wavers more towards one end than the other, or if it is evenly spread.
- For \(p = 0.1\), the skewness occurs to the right, indicating that fewer successes are more likely. This is because with a low probability, the chance of achieving success in multiple trials is minimal.
- A probability of \(p = 0.9\) causes left skewness. In this scenario, the probability favors a higher number of successes, so the most probable outcomes are clustered on the higher side.
Symmetry in Distributions
Symmetry in a probability distribution indicates that the distribution is balanced around its central point. In a binomial distribution, symmetry typically occurs when the probability of success in each trial is 0.5.
When the probability (
p
equals 0.5, each trial outcome has an equal chance of being a success or a failure. This creates a symmetric distribution where the probability of having a particular number of successes is mirrored on both sides of the mean at 2.5.
This type of uniformity simplifies analysis and interpretation:
- It facilitates the use of statistical inferencing techniques that assume normality.
- It allows for easier comparison between different sets of data or different probability models.