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Suppose that 10 patients with meningitis received treatment with large doses of penicillin. Three days later, temperatures were recorded, and the treatment was considered successful if there had been a reduction in a patient's temperature. Denoting success by \(\mathrm{S}\) and failure by \(\mathrm{F}\), the 10 observations are \(\begin{array}{llllllllll}\mathrm{S} & \mathrm{S} & \mathrm{F} & \mathrm{S} & \mathrm{S} & \mathrm{S} & \mathrm{F} & \mathrm{F} & \mathrm{S} & \mathrm{S}\end{array}\) a. What is the value of the sample proportion of successes? b. Replace each \(\mathrm{S}\) with a 1 and each \(\mathrm{F}\) with a 0 . Then calculate \(\bar{x}\) for this numerically coded sample. How does \(\bar{x}\) compare to \(p ?\) c. Suppose that it is decided to include 15 more patients in the study. How many of these would have to be S's to give \(p=.80\) for the entire sample of 25 patients?

Short Answer

Expert verified
a) The sample proportion of successes is 0.7 or 70%. b) After replacing each \(S\) with a 1 and each \(F\) with a 0, the calculated mean for this coded sample is also 0.7 or 70%; thus, \(\bar x\) is equal to \(p\). c) To achieve a success proportion of 0.80 or 80% for the entire sample of 25 patients, 13 out of the 15 new patients would have to be successes.

Step by step solution

01

Calculation of Sample Proportion of Successes

First count the number of successes (\(S\)) in the given sample. There are 7 successes. The sample size is 10. Thus, the sample proportion of successes, denoted \(p\), is calculated as \(p = \text{number of successes} / \text{sample size} = 7 / 10 = 0.7\) or 70%.
02

Numerical Coding of Sample and Mean Calculation

Replace each \(S\) with a 1 and each \(F\) with a 0. The new numerically encoded sample is: 1, 1, 0, 1, 1, 1, 0, 0, 1, 1. To calculate the sample mean, \(\bar x\), sum all these values and divide by the sample size. \(\bar x = (1 + 1 + 0 + 1 + 1 + 1 + 0 + 0 + 1 + 1) / 10 = 7 / 10 = 0.7\) or 70%. It can be observed that \(\bar x\) equals \(p\).
03

Proportional Predictive Calculation

For the sample to have a proportion of successes, \(p = .80\) or 80%, with 25 patients in total (the original 10 plus 15 new), the total number of successes needed is \(0.80 * 25 = 20\). So, subtract the number of successes from the original sample from this total to find the necessary number of successes among the new patients: \(20 - 7 = 13\). Therefore, 13 of the 15 new patients would have to be successes.

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Key Concepts

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

Statistical Inference
Understanding statistical inference is crucial when analyzing data from studies or experiments. This process involves making conclusions about a population based on sample data. In the context of our exercise, we infer about the effectiveness of penicillin in treating meningitis by examining the outcomes (successes or failures) in a small group of patients.

Statistical inference typically includes estimating population parameters (like the proportion of success in our case), testing hypotheses, and making predictions. To estimate the population parameter, we often use a sample statistic—here, the sample proportion, denoted as \(p\), is calculated by dividing the number of observed successes by the sample size. The key is to ensure that the sample is representative of the population, otherwise, the inference may not be valid.

Moreover, confidence intervals and hypothesis testing are common methods in statistical inference. They help in assessing the reliability of our estimates and in determining whether there's a statistically significant effect. However, these concepts extend beyond the scope of this particular exercise.
Binomial Distribution
The binomial distribution provides a theoretical model for the type of data we observe in this exercise. It describes the number of successes in a fixed number of independent trials, where each trial results in either a success or a failure, and the probability of success is the same for each trial.

In the presented problem, the reduction of temperature after treatment is considered a success and we have a fixed number of ten trials (patients). If we assume that each patient's response to the treatment is independent and the probability of success is constant, the data follows a binomial distribution.

The sample size (10 patients) and the number of successes (7 successes) can be used to estimate the probability of success, which is a parameter of the binomial distribution. This estimated probability is also the sample proportion, \(p\), and in the context of binomial distribution, it approximates the 'true' success probability of the penicillin treatment for the given condition, assuming a large enough sample size and representative sampling.

Understanding binomial distribution is essential in predicting future outcomes and calculating probabilities for different numbers of successes in similar trials. This, in turn, helps in planning studies and interpreting their results.
Data Analysis
Data analysis is the cornerstone of research, providing insights and supporting decision-making. It involves inspecting, cleansing, transforming, and modelling data with the goal of discovering useful information, suggesting conclusions, and supporting decision-making.

In our exercise, the analysis begins with coding the data, which simplifies the interpretation and computation. Replacing each 'success' (S) with 1 and 'failure' (F) with 0 is an example of such coding. This numerical representation aids in calculating summary statistics like the sample mean, \(\bar{x}\), which in this case, confirms the sample proportion, \(p\).

The data analysis does not stop at calculating the mean or proportion; it often involves complex computations and interpretations. One might be interested in assessing the variability of the data through standard deviation or variance, or in making predictions for future data, as illustrated by the need to calculate how many successes among 15 new patients would result in an overall success rate of 80%. The focus is on turning raw data into knowledge that can guide actions, such as adjusting treatment protocols or expanding research studies.

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