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The presence of bacteria in a urine sample (bacteriuria) is sometimes associated with symptoms of kidney disease in women. Suppose a determination of bacteriuria has been made over a large population of women at one point in time and \(5 \%\) of those sampled are positive for bacteriuria. If a sample size of 5 is selected from this population, what is the probability that 1 or more women are positive for bacteriuria?

Short Answer

Expert verified
The probability is approximately 22.6%.

Step by step solution

01

Understand the Probabilities

The general probability of finding a woman positive for bacteriuria in the population is given as 5%, which translates to a probability of 0.05. Consequently, the probability of a person not having bacteriuria is 0.95 (because 1 - 0.05 = 0.95).
02

Define the Problem

We're asked to find the probability that in a random sample of five women, at least one woman is positive for bacteriuria.
03

Probability of Zero Positives

First, let's calculate the probability that none of the 5 women have bacteriuria. This is the same as all 5 women being negative, which is calculated as: \[ P(0 \text{ positive}) = 0.95^5 \]
04

Calculate Zero Positives Probability

Now compute the probability: \[ 0.95^5 = 0.7737809375 \].
05

Calculate Probability of At Least One Positive

We need the probability that at least one is positive. This can be found by subtracting the probability of zero positives from 1:\[ P(\text{at least 1 positive}) = 1 - P(0 \text{ positive}) = 1 - 0.7737809375 \]
06

Final Calculation

Compute the probability of at least one positive:\[ 1 - 0.7737809375 = 0.2262190625 \]
07

Conclusion

Thus, the probability that 1 or more women are positive for bacteriuria in a sample of 5 is approximately 0.226 or 22.6%.

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Key Concepts

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

Probability
Probability is a fundamental concept in statistics that measures the likelihood of a certain event happening. In simple terms, it's a way to quantify uncertainty or the chance of different outcomes. When we say there's a 5% chance of an event, it means that in a large number of trials, that event will occur about 5% of the time.

In our exercise related to bacteriuria, the probability that a randomly selected woman from the population has bacteriuria is 0.05, or 5%. On the flip side, the probability that a woman does not have bacteriuria is 0.95. To calculate the probability of one or more women in a sample having bacteriuria, we found the probability of none having it and subtracted this from 1. This is because the two scenarios (none having bacteriuria and at least one having it) account for all possibilities and together sum to 1.

Understanding probability helps in decision-making and evaluating the likelihood of various outcomes, making it crucial in fields ranging from healthcare to finance.
Bacteriuria
Bacteriuria refers to the presence of bacteria in urine, which can be an indicator of a urinary tract infection or other medical conditions, including kidney disease. For accurate medical diagnosis, urine samples are typically tested for bacteriuria, which can often lead to symptoms like frequent urination or discomfort.

In our case, knowing the prevalence of bacteriuria in the population (5%) allows us to make informed predictions about health risks within a sample size. Such information is important for healthcare providers to decide on screening or preventive measures, especially in populations where bacteriuria is associated with more serious conditions.

It's not just about treating current infections but also about understanding the spread and risk factors associated with bacteriuria, leading to better public health strategies and patient outcomes.
Sample Size
Sample size is a critical factor in statistical studies as it influences the reliability and accuracy of results. The sample size refers to the number of observations or participants included in a study or survey. In biostatistics, choosing an appropriate sample size is key because it affects the statistical significance and the power of a study's findings.

In our exercise, the sample size is 5 women from a larger population. Some may wonder why it's important to calculate outcomes based on a sample rather than the whole population. The practical reason is that analyzing an entire population is often not feasible, so smaller, manageable samples are used to make inferences about the population.

When deciding on a sample size, one should consider the available resources, the scope of the study, and the desired level of accuracy. Choosing the right sample size ensures that conclusions drawn from the sample closely reflect the reality in the broader population.

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Most popular questions from this chapter

A study was conducted among 234 people who had expressed a desire to stop smoking but who had not yet stopped. On the day they quit smoking, their carbonmonoxide level (CO) was measured and the time was noted from the time they smoked their last cigarette to the time of the CO measurement. The CO level provides an "objective" indicator of the number of cigarettes smoked per day during the time immediately before the quit attempt. However, it is known to also be influenced by the time since the last cigarette was smoked. Thus, this time is provided as well as a "corrected CO level," which is adjusted for the time since the last cigarette was smoked. Information is also provided on the age and sex of the participants as well as each participant's self-report of the number of cigarettes smoked per day. The participants were followed for 1 year for the purpose of determining the number of days they remained abstinent. Number of days abstinent ranged from 0 for those who quit for less than 1 day to 365 for those who were abstinent for the full year. Assume all people were followed for the entire year. (TABLE CAN NOT COPY) Develop a life table similar to Table 4.16, giving the number of people who remained abstinent at \(1,2, \ldots\) 12 months of life (assume for simplicity that there are 30 days in each of the first 11 months after quitting and 35 days in the 12 th month). Plot these data on the computer using either Excel or \(R\) or some other statistical package. Compute the probability that a person will remain abstinent at \(1,3,6,\) and 12 months after quitting.

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