Which one of the following statements regarding the normal distribution is correct?
Correct Answer C:
The Normal distribution is a continuous probability distribution.
Normal distribution:
The normal distribution is also known as the Gaussian distribution or 'bell-shaped' distribution. It describes the spread of many biological and clinical measurements.
Properties of the Normal distribution:
Standard deviation:
Which one of the following would cause a fall in the carbon monoxide transfer factor (TLCO)?
Transfer factor:
The transfer factor describes the rate at which a gas will diffuse from alveoli into blood. Carbon monoxide is used to test the rate of diffusion. Results may be given as the total gas transfer (TLCO) or that corrected for lung volume (transfer coefficient, KCO).
KCO also tends to increase with age.
Some conditions may cause an increased KCO with a normal or reduced TLCO:
Chronic lymphocytic leukaemia is mostly due to a:
Correct Answer B:
CLL is caused by a monoclonal proliferation of B-cell lymphocytes.
Chronic lymphocytic leukaemia:
Chronic lymphocytic leukaemia (CLL) is caused by a monoclonal proliferation of well-differentiated lymphocytes which are almost always B-cells (99%).
Features:
Complications:
Investigations:
A new blood test which can show signs of myocardial damage within one hour of the onset of chest pain is developed. In a trial of 100 patients presenting with chest pain, 40 of the patients are later proven to have had myocardial ischaemia by conventional troponin tests. Of these patients the new test was positive in 20 cases. The new test was also positive in 20 of the remaining 60 patients later shown to have a negative troponin.
What is the negative predictive value of the new test for myocardial ischaemia?
The new test was negative in 20 of the patients later shown to have myocardial ischaemia (false negative) and negative in 40 patients confirmed not to have myocardial ischaemia (true negative)
Negative predictive value = TN / (TN + FN) = 40 / (40 + 20) = 0.66
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.
You are a ST1 doctor on a gastroenterology ward. The F2 doctor has asked you to supervise him putting in an ascitic drain for a patient with liver cirrhosis. He is keen to get it signed off for his portfolio. He has never seen one put in before but has read around the subject.
What is the most appropriate action?
It used to be said that for procedures 'see one, do one, teach one'. These days have long gone. Doctors are now expected to show proof of competency before performing procedures alone. In this scenario the F2 doctor has never seen one previously so it is not appropriate for him to insert the drain today. The best option is for him to watch you.
If you are going to let the F2 doctor insert the drain you should be honest with the patient about his lack of experience.
Signing him off without seeing him perform the procedure is a very poor option which could result in a GMC referral if found out. It also puts future patients at risk.
Letting him insert the drain today without supervision is again a very poor option as it puts the patient at risk.
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