Question

Base questions 7-9 on the following information: Pulse Oximetry is a small device that attaches painlessly to the fingertip, using lightwaves to measure pulse rate and oxygen levels. Researchers examined the use of pulse oximetry in young children in rural resource-poor areas to identify children with severe illnesses, particularly pneumonia, who need to be sent to the hospital. The study examined several cut-points for oxygen saturation, below which the child will be considered to have severe pnemonia. The gold standard for diagnosing severe illness/pneumonia were by using clinical criteria. For a cut-point of 94%, the sensitivity was 28%, specificity 92%, PPV=23%, NPV=93%.

Assuming the researcher recruits a large random sample of young children, what is the NPV expressed in terms of numerator and denominator (using the cutpoint of 95%)?

a.The numerator is the number of children with oxygen saturation below 95% and who are severely ill. The denominator is the number of children who are severely ill.

b. The numerator is the number of children with oxygen saturation below 95% and who are not severely ill. The denominator is the number children with oxygen saturation at or above 95%

c.The numerator is the number of children with oxygen saturation below 95% and who are not severaly ill. The denominator is the number of children who are not severely ill.

d. The numerator is the number of children with oxygen saturation at or above 95% and who are not severely ill. The denominator are the number of children with oxygen saturation at or above 95%

Answer 1

NPV = True Negative / (True Negative + False Negative)

So, numerator is True Negative cases which is number of children with oxygen saturation at or above 95% and who are not severely ill.

Denominator is sum of True Negative and False Negative which is all negative cases of the test and are the number of children with oxygen saturation at or above 95%.

Thus, the answer is

d. The numerator is the number of children with oxygen saturation at or above 95% and who are not severely ill. The denominator are the number of children with oxygen saturation at or above 95%