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## Introduction to Sensitivity and Risk

Discuss about the Introduction to Clinical Epidemiology for Negative Throat Culture.

Answer questions 6a-c based on the following information: A total of 1500 children have a rapid strep test (RST) done by a standardized culture technique. Of the 1500 children, 1338 have a negative RST and 162 have a positive RST. In addition, a backup throat culture (gold standard) was done on all children. Of those children with a negative RST, 1302 have a negative throat culture. In the group with a positive RST, 159 have a positive throat culture.

Q6: Construct a 2x2 table using the information provided above, and answer the following questions (a-c):

A 2x2 table

 Target disorder (strep tonsillitis) Present Absent Totals Diagnostic Test Result Positive RST 159 3 162 Negative RST 36 1302 1338 195 1305 1500

Calculate the sensitivity of the RST [2 marks]

Sensitivity= TP/ (TP+FN)

Sensitivity = 159/ (159+36)

Sensitivity = 159/195

= 0.815

=81.5%

1. Calculate the specificity of the RST [2 marks]

Specificity = TN/ (FP+TN)

Specificity = 1302/ (3+1302)

Specificity = 1302/ 1305

= 0.997

= 99.7%

1. Calculate the positive predictive value of the RST [2 marks]

The positive predictive value is given by the probability of the disease among patients with a positive test.

PPV= TP/ (TP+FP)

=159/ (159+3)

=159/162

=0.9815

= 98.15%

1. In a test with high sensitivity, a negative result rules in the diagnosis [True/False] [1 marks]

True

1. In a test with high specificity, a positive result rules out the diagnosis [True/False] [1 marks]

True

1. The positive predictive value is dependent on all of the following: prevalence, incidence, sensitivity and specificity [True/False] [1 mark]

True

1. Using the image below, which value in the test result units is the point of maximum specificity. [1 mark]
1. a) 20 b) 15 c) 5 d) 30 e) 25 The point of maximum specificity = 30

Answer questions 7a-d based on the following information:

Saag et al. Romosozumab or Alendronate for Fracture Prevention in Women with Osteoporosis. N Engl J Med 2017; 377:1417-1427

Romosozumab is a monoclonal antibody that binds to and inhibits sclerostin, increases bone formation, and decreases bone resorption

Methods: We enrolled 4093 postmenopausal women with osteoporosis and a fragility fracture and randomly assigned them in a 1:1 ratio to receive monthly subcutaneous romosozumab (210 mg) or weekly oral alendronate (70 mg) in a blinded fashion for 12 months, followed by open-label alendronate in both groups. The primary end points were the cumulative incidence of new vertebral fracture at 24 months and the cumulative incidence of clinical fracture (nonvertebral and symptomatic vertebral fracture) at the time of the primary analysis (after clinical fractures had been confirmed in ≥330 patients). Secondary end points included the incidences of nonvertebral and hip fracture at the time of the primary analysis. Serious cardiovascular adverse events, osteonecrosis of the jaw, and atypical femoral fractures were adjudicated.

Conclusions:

In postmenopausal women with osteoporosis who were at high risk for fracture, romosozumab treatment for 12 months followed by alendronate resulted in a significantly lower risk of fracture than alendronate alone.

## Calculating Sensitivity

Q7a. Construct a 2x2 table using the information in the abstract, and answer the following questions:

 MI Total Yes No Romosozumab-to-alendronate 127 1919 2046 Alendronate-to –alendronate group 243 1804 2047 Total 370 3723 4093

What is the risk of developing clinical fractures in all patients included in the study? [2 marks]

Risk = 370/4093

= 0.0904

=9.04%

• What is the risk of developing clinical fractures in patients who received romosozumab-to-alendronate treatment [2 marks]?

Risk = 127/2046

= 0.06207

= 6.2%

• What is the risk of developing clinical fractures in patients who received alendronate-to-alendronate treatment? [2 marks]

Risk = Risk = 243/2047

= 0.1187

= 11.9%

• What is the relative risk of treatment with romosozumab-to-alendronate versus alendronateto-alendronate with regard to experiencing clinical fractures? How would you interpret this relative risk estimate? [4 marks]

Relative risk = 6.2/11.9

= 0.521

= 1:2

This implies that for one single risk of treatment with romosozumab-to-alendronate, there will be two cases of risks of treatment with alendronateto-alendronate.

Q7b. If equal numbers of patients in the population received romosozumab-to-alendronate vs alendronate-to-alendronate treatment, what would be the expected population relative risk reduction (RRR) for romosozumab-to-alendronate treatment? How would you interpret this measure? [4 marks]

Relative risk reduction =

Risk of Alendronateto-alendronate = 127/2047

= 6.2%

Expected population relative risk = 254/4093

=6.2%

Reduction = 9.04%-6.2%

= 2.8%

Q7c. How many patients need to be treated with romosozumab-to-alendronate regimen for one more patient to be benefit compared with the alendronate-to-alendronate regimen? What is this measure called? How would you interpret this measure [2 marks]?

The number of patients to be treated = 243-127+1

= 117 patients

The measure is called a balancing out measure where an extra sample will benefit from the calculation.

Q7d. How does the measure in question 7b differ from question 7c? [2 marks]

In question 7b, the measure is based on ratio where the relative value is obtained while in the later the measure is based on balancing out of values.

Read the attached original research article (Keenan et al., 2018), available in vUWS), and now answer Questions 8 to 10:

Q8. What characteristics of the study would you consider in order to determine if its findings are valid? Include wider considerations of study quality/validity and give examples. (Q8 will address relevance, and the next question will ask how to determine the importance of the findings...for this question, focus on the internal validity of the study) [16 marks]

Validity in research refers to the believability or the credibility of the findings of the research (Ary et al., 2018). It involves genuineness of the results or the findings and it has two aspects; internal and external validity. For the case study, we will consider the internal validity of the research, which is composed of the procedures or instruments, which are used in the research that they were supposed to measure. For example, in the research article, the results obtained of a twelve-month interim analysis for efficacy did not meet the criterion that was prespecified for the early stopping (Eng et al., 2018, pp.199-209). However, the estimation that was based on assumptions in the partial findings was not catered for in the final findings of the research article. This brings the question of validity of the findings in place, as the relevance of quality and validity are not considered.

## Calculating Specificity

In the research article, the relevance of validity would ensure that the results are not deemed thus making the findings meaningful and reliable. If the study does not provide a measure of what is supposed to measure then the findings will not be conclusive in answering the research study questions. Validity helps qualify the research findings to the research questions and helps to answer the aims and objectives that were outlined for study. If there is any doubt or absence of certain critical information that is aimed at explaining the information in the findings the results will be considered in accurate and the researched said to lack validity (Steenks et al., 2018).

Q9. What characteristics of the findings would you consider, in order, to determine if they are clinically meaningful and statistically significant? Include examples. (You’ve already addressed validity…for this question, focus on how to determine the clinical significance and statistical significance of an effect reported in the study) [8 marks]

Statistical significance is when the results of the selected sample are applied to another population (Benjamin et al., 2018, p.6). However, a concern arises whether the results of the given sample will give the required objectives or will provide misleading information. Moreover, clinical significance is when the magnitude of previous treatment is applied to the current patients as a guideline in offering the treatment to the later patients. In the efforts to determine the clinical and statistical significance, a lot of effort should be put in to determine any source of biases that is supposed to be removed in order to re-align the samples’ results in an accurate as much as possible (Nardi, 2018). The testing of significance in the research article is centred about the likelihood of a chance that will not be a hold up in the future replications whereby all the possible hindrances to the accuracy of the results are minimized.

Q10. What characteristics of the study would you consider, in order, to determine if it is generalizable to your context? Explain your answers and provide examples. (Questions 6 and 7 have asked how to determine if the study is valid, and how important the findings are....for this question, focus on how to determine if it is really relevant or generalizable to your practice.) [8 marks]

Generalization is the interpolation of a certain finding of the past to the current study. Generalization can be useful in cases where there is no enough data or evidence to support the hypothesis. It can be said to be based on the probability of accuracy, which can result in very misleading findings or accurate findings (Hopp et al., 2018, pp.458-487). In this context, generalization of the results is more accurate since the data obtained and the methods used in calculating provides an accurate measure of results thus making it viable to say the  generalization would result to an accurate finding.

References

Ary, D., Jacobs, L. C., Irvine, C. K. S., and Walker, D., 2018. Introduction to research in education. s.l.:Cengage Learning.

Benjamin, D. J., Berger, J. O., Johannesson, M., Nosek, B. A., Wagenmakers, E. J., Berk, R. and Cesarini, D., 2018. Redefine statistical significance. Nature Human Behaviour, 2(1), p. 6.

Eng, Q. D., Yang, H., Lievens, F., & McDaniel, M. A., 2018. Optimizing the validity of   situational judgment tests: The importance of scoring methods. Journal of Vocational   Behavior, Volume 104, pp. 199-209.

Hopp, C., Antons, D., Kaminski, J., & Salge, T. O., 2018. The Topic Landscape of Disruption Research—A Call for Consolidation, Reconciliation, and Generalization. Journal of    Product Innovation Management, 35(3), pp. 458-487.

Nardi, P. M., 2018. Doing survey research: A guide to quantitative methods. s.l.:Routledge.

Steenks, M. H., Türp, J. C., and Wijer, A., 2018. Reliability and Validity of the Diagnostic  Criteria for Temporomandibular Disorders Axis I in Clinical and Research Settings: A Critical Appraisal. Journal of Oral & Facial Pain & Headache, 32(1).

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250 words