A laboratory balance used in a nutrition survey weighs every child exactly 500 g less than their true weight, and repeated weighings of the same child give identical readings. This instrument is best described as:

• A Both valid and reliable
• B Reliable but not valid ✓
• C Valid but not reliable
• D Neither valid nor reliable

Explanation

Reliability, or precision, is the ability of a test to give consistent results on repetition, while validity, or accuracy, is the ability to measure what it is supposed to measure, that is closeness to the true value. The scale reproduces the same reading every time, so it is reliable, but every reading is systematically off by 500 g, so it is not valid. This illustrates that a test can be precise yet inaccurate due to systematic error or bias.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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