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Medical risks Morris’s kidneys are failing, and he is awaiting a kidney transplant. His doctor gives him this information for patients in his condition: 90% survive the transplant and 10% die. The transplant succeeds in 60% of those who survive, and the other 40% must return to kidney dialysis. The proportions who survive five years are 70% for those with a new kidney and 50% for those who return to dialysis. (a) Make a tree diagram to represent this setting. (b) Find the probability that Morris will survive for five years. Show your work.

Short Answer

Expert verified
Morris has a 55.8% probability of surviving for five years.

Step by step solution

01

Understand the Scenario

We are given the probabilities of different outcomes related to Morris's kidney treatment. We need to represent these probabilities in a tree diagram to visualize the different paths and calculate the overall probability of Morris surviving for five years.
02

Draw the Tree Diagram

Start by drawing a main branch from the initial state. From this branch, split into two outcomes: 'Surgery Survives' with a probability of 0.9 and 'Surgery Dies' with a probability of 0.1. Then, for 'Surgery Survives,' split into two more branches: 'New Kidney' with a probability of 0.6, and 'Return to Dialysis' with a probability of 0.4.
03

Extend the Tree Diagram with Five-Year Survival

For both the 'New Kidney' and 'Return to Dialysis' branches, extend them further to show five-year survival. So, from 'New Kidney,' branch into 'Survive 5 Years' with a probability of 0.7, and 'Not Survive 5 Years' with a probability of 0.3. Similarly, from 'Return to Dialysis,' branch into 'Survive 5 Years' with a probability of 0.5, and 'Not Survive 5 Years' with a probability of 0.5.
04

Calculate Probabilities for Each Path

Calculate the final probabilities for each outcome of interest: - Probability of surviving 5 years with a new kidney: \( P(\text{Survive 5 Years With New Kidney}) = 0.9 \times 0.6 \times 0.7 = 0.378 \).- Probability of surviving 5 years with dialysis: \( P(\text{Survive 5 Years With Dialysis}) = 0.9 \times 0.4 \times 0.5 = 0.18 \).
05

Add the Probabilities for Five-Year Survival

To find the overall probability that Morris survives five years, sum the probabilities of all successful paths: \[ P(\text{Survive 5 Years}) = P(\text{Survive 5 Years With New Kidney}) + P(\text{Survive 5 Years With Dialysis}) = 0.378 + 0.18 = 0.558 \].
06

Interpret the Result

The probability of Morris surviving for five years, given the different possible outcomes, is represented by the calculated probability. This represents the culmination of Morris either getting a new kidney or continuing dialysis each with their chances of survival.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Tree Diagram
A tree diagram is a visual representation of all possible pathways or outcomes of an event. In the context of medical statistics and probability, a tree diagram provides a clear map of each possible outcome following a medical procedure, revealing the choices and their respective probabilities. By starting from a single point, a tree diagram branches out for each decision or result, allowing you to display sequential events and their probabilities.

For Morris’s kidney transplant scenario, a tree diagram helps in organizing the series of events from surgery to potential survival outcomes over five years. We begin with two main branches indicating whether Morris survives the surgery or not. Each branch then divides further based on subsequent events, such as receiving a new kidney or returning to dialysis and their respective survival probabilities. This structured format facilitates the computation of complex probabilities by simplifying the visualization of paths, helping us reach calculated probabilities for final outcomes.

Using a tree diagram not only streamlines the data but offers a straightforward logical approach to complex probability questions. This is particularly important in medical scenarios where understanding the impact of a series of outcomes can be critical.
Conditional Probability
Conditional probability is the likelihood of an event occurring given that another event has already taken place. It is crucial in medical statistics, where outcomes are dependent on previous results or conditions.

In Morris's situation, once he survives surgery, the probability of further outcomes like receiving a new kidney or returning to dialysis becomes conditional upon surviving the initial surgery. Conditional probabilities are calculated using the formula:

\[ P(A|B) = \frac{P(A \cap B)}{P(B)} \]

Where \( P(A|B) \) is the probability of event A occurring given B is true, \( P(A \cap B) \) denotes the probability of both events A and B occurring, and \( P(B) \) is the probability of event B.

In our example, once it is established that Morris survives the surgery (90% or 0.9 probability), the next conditional probabilities are evaluated for the subsequent paths of treatment and survival. For those who survive, the probability of getting a new kidney (60% or 0.6) is contingent on this previous event. Conditional probability helps unravel the complexities of uncertain medical outcomes based on preceding conditions, making it a powerful tool in health-related decision-making.
Medical Statistics
Medical statistics apply statistical methods to understand and solve problems in health and medicine. They are key in clinical decision-making and risk analysis.

In Morris’s case, medical statistics inform us about the likelihood of surviving a transplant, succeeding with a new kidney, or continuing on dialysis. Such statistics provide a basis for predicting outcomes and guiding treatment plans.
  • Statistical data aids doctors in assessing treatment risks and benefits.
  • They support decisions about whether a patient should undergo a particular procedure or continue alternative therapies.
Medical statistics like Morris's probabilities—90% for survival post-surgery, 60% chance of successful transplantation, and respective survival rates for each renal treatment—help communicate the scenario's possible trajectories.

It converts raw medical data into valuable insights, aiding patients and healthcare providers in making informed decisions. Recognizing the power of statistics in medicine enhances understanding of health patterns, improving outcomes and advancing research in the medical field.

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