What is the specificity of sputum microscopy in detection of Pulmonary Tuberculosis (PTB) as per the information given below?
PTB Total Sputum microscopy Present Absent Positive 270 20 290 Negative 30 180 210 Total 300 200 500
To calculate the specificity of sputum microscopy in the detection of Pulmonary Tuberculosis (PTB), we need to understand the concept of specificity. Specificity is defined as the ability of a test to correctly identify those without the disease (true negatives) from all those who do not have the disease.
The formula for specificity is given by:
\(\text{Specificity} = \frac{\text{True Negatives (TN)}}{\text{True Negatives (TN) + False Positives (FP)}} \times 100\)%
From the table:
- True Negatives (TN) = 180 (Sputum microscopy is negative and PTB is absent)
- False Positives (FP) = 20 (Sputum microscopy is positive but PTB is absent)
Substituting these values into the formula, we have:
\(\text{Specificity} = \frac{180}{180 + 20} \times 100\)% = \(\frac{180}{200} \times 100\)% = 90%
Thus, the specificity of sputum microscopy in detecting PTB is 90%.
Let's briefly analyze the options provided:
10%
- : Too low; would suggest poor test performance in correctly identifying those without the disease.
36%
- : Higher than 10% but still indicates poor specificity.
90%
- : Correct; matches our calculations, indicating high specificity.
94%
- : Incorrect; this value is higher than what we calculated.
This confirms that the correct answer is indeed 90%.
Important Questions from Biostatistics
In a cohort of 500 women attending antenatal clinic, 70 % had ultrasonography (USG). This cohort was followed up at delivery. Of the women who had USG, 70 delivered low birth weight (LBW) babies; whereas of the women, who did not undergo USG, 50 delivered LBW babies. The incidence of LBW babies among women who had USG is:
In a case-control study, 300 women aged 20-45 years suffering from breast cancer were compared with age-matched 300 women without breast cancer. It was observed that 120 women among cases and 60 women among controls were obese. The odds ratio of developing breast cancer among obese women is:
What is the relative risk of developing pulmonary embolism in users of oral contraceptives as per the information given below?
Women using OCs Pulmonary embolism Total Yes No Yes 120 80 200 No 10 70 80 Total 130 150 280 Which one of the following tests should be applied to compare mean haemoglobin level of two groups of antenatal mothers?
- The following table shows the mortality figures among hazardous industry workers :
Age group National death rate per 1000 Hazardous industry worker population Observed deaths 25-34 2.0 3000 8 35-44 3.5 2000 9 45-54 6.0 2000 13
What is the Standardized Mortality Ratio (SMR) for the hazardous industry workers (as compared to national popu-lation) ?
