Scale reads 75 kg (true = 68 kg) 20 times. Description?

Question

Scale reads 75 kg (true = 68 kg) 20 times. Description??  
A. Valid, not reliable  
B. Reliable, not valid  
C. Both  
D. Neither

Accepted Answer

Correct Answer: (B)Reliable, not valid. 
Rationale: The scale's measurements are reliable but not valid.In measurement theory, reliability refers to the consistency or repeatability of a measurement tool. A reliable instrument yields very similar results when the same quantity is measured repeatedly under unchanged conditions. Validity refers to the accuracy of the measurement, how closely the measured value aligns with the true or accepted value. A valid instrument measures what it is intended to measure without systematic bias. In this scenario, the scale reads 75 kg every single time out of 20 trials. This demonstrates exceptional consistency and a complete absence of random error, which defines high reliability. However, the true mass is 68 kg. The scale's consistent reading is 7 kg higher than the true value, indicating a persistent, systematic error (bias). This means the scale is not accurate; it does not provide a valid measurement of the actual mass.A) Valid, not reliableThis describes an instrument that is accurate on average but gives inconsistent readings. For example, if readings were 68, 72, 65, and 69 kg (averaging close to 68), it would be somewhat valid but not reliable. The scale in question shows the opposite pattern: perfect consistency but gross inaccuracy.B) Reliable, not validThis accurately describes the situation. The scale's output is perfectly consistent (reliable), as it gives the same result repeatedly. However, its consistent result is far from the true value (invalid). This indicates a calibration error or a systematic bias in the measuring mechanism.C) BothFor an instrument to be both valid and reliable, it must be both accurate and consistent. It would need to read very close to 68 kg every time. Since the scale consistently reads 75 kg, it lacks validity and therefore cannot be both.D) NeitherAn instrument that is neither valid nor reliable would produce inconsistent readings that also do not center around the true value. For example, readings of 60, 80, 55, and 85 kg would be neither reliable (high variability) nor valid (not near 68 kg). The given scale is highly reliable, so this option is incorrect.ConclusionThe concepts of reliability and validity are distinct. Reliability is about precision and repeatability, while validity is about accuracy and truthfulness. A measuring device can be reliable without being valid if it has a consistent bias. The scale's perfect consistency across 20 trials confirms high reliability, but its significant and constant deviation from the known true value confirms a lack of validity.

Scale reads 75 kg (true = 68 kg) 20 times. Description?

A
Valid, not reliable

B
Reliable, not valid

C
Both

D
Neither

The scale's measurements are reliable but not valid.

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Scale reads 75 kg (true = 68 kg) 20 times. Description?

A Valid, not reliable B Reliable, not valid C Both D Neither

The scale's measurements are reliable but not valid.

Topic Flashcards

Mini Quiz

Related Questions

A
Valid, not reliable

B
Reliable, not valid

C
Both

D
Neither