Antibody titres against dengue virus in a group of patients are recorded as 1:10, 1:20, 1:40, 1:40 and 1:640. The values rise by doubling steps and the distribution is highly skewed to the right. Which average best summarises these titre values?
- A Arithmetic mean
- B Median
- C Geometric mean ✓
- D Harmonic mean
Correct answer: C. Geometric mean
Explanation
Serial antibody titres are log-normally distributed because they increase in doubling dilutions, so averaging the log-transformed values gives the geometric mean, which is the conventionally reported average for titres in serology. The arithmetic mean would be pulled upward by the single 1:640 outlier and does not correspond to any actual dilution step, making it inappropriate here despite being computable.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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