Which one of the following statements regarding odds and odds ratio is correct?
Correct Answer C:
Odds and odds ratio: Odds are a ratio of the number of people who incur a particular outcome to the number of people who do not incur the outcome. The odds ratio may be defined as the ratio of the odds of a particular outcome with experimental treatment and that of control.
Odds ratios are the usual reported measure in case-control studies. It approximates to relative risk if the outcome of interest is rare. For example, if we look at a trial comparing the use of paracetamol for dysmenorrhoea compared to placebo we may get the following results:
In terms of the cell cycle, mitosis takes place in:
Correct Answer A:
Cell cycle:
What is the correct formula to calculate the positive predictive value?
TP = true positive; FP = false positive; TN = true negative; FN = false negative
Correct Answer B: Positive predictive value = TP / (TP + FP)
Screening test statistics It would be unusual for a medical exam not to feature a question based around screening test statistics. The available data should be used to construct a contingency table as below: TP = true positive; FP = false positive; TN = true negative; FN = false negative
The table below lists the main statistical terms used in relation to screening tests:
Positive and negative predictive values are prevalence dependent. Likelihood ratios are not prevalence dependent.
A randomized controlled trial is performed to look at a new drug to prevent hip fractures in postmenopausal women. Group A consists of 1,000 women who take the new drug whilst group B contains 1,400 women taking a placebo. The hip fracture rate in group A is 2% and in group B is 4%.
What is the number needed to treat to prevent one hip fracture?
Correct Answer B: NNT = 1 / Absolute Risk Reduction
They key to answering this question is to ignore irrelevant data such as the number of patients in each group.
Numbers needed to treat and absolute risk reduction:
Numbers needed to treat (NNT) is a measure that indicates how many patients would require an intervention to reduce the expected number of outcomes by one It is calculated by 1/(Absolute risk reduction) and is rounded to the next highest whole number.
Experimental event rate (EER) = (Number who had particular outcome with the intervention) / (Total number who had the intervention).
Control event rate (CER) = (Number who had particular outcome with the control/ (Total number who had the control).
Absolute risk reduction = CER-EER or EER-CER?
The absolute risk reduction (ARR) may be calculated by finding the absolute difference between the control event rate (CER) and the experimental event rate (EER). You will often find both versions of the above listed in different sources. In some ways in doesn't matter which you use as you will end up with the same answer but from a technical point of view:
*this may be more accurately termed absolute benefit increase, rather than absolute risk reduction
Where is the majority of iron found in the body?
Correct Answer B:
Iron metabolism:
Absorption:
Distribution in body:
Transport:
Storage:
Excretion:
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