Question

Part 1: Validity, bias, reliability. a) This winter I went to a local pharmacy to have my weight and blood pressure measured using a sophisticated electronic machine at the front of the store next to the checkout counter. Will the measurement of my weight be biased? Will it be reliable? Will it be valid? Explain your answers. b) Give your own example of a measurement process that is valid but has large bias. c) Give your own example of a measurement process that is invalid but highly reliable.

Answer 1

Note:

Hey there! Thank you for the question. The questions in Part (a) are related. However, the questions in Parts (b) and (c) are independent of the questions in Part (a), although based on the same concept. Hence, according to our policy, we have answered the first question, that is, Part (a) for you.

(a)

Bias: Bias can be defined as a systematic error in the representation of a population by a sample from it.

Reliability: Reliability can be defined as the degree to which, the results of a test are consistent, when the trials are conducted repeatedly.

Validity: Validity can be defined as the degree to which, a test correctly asses the actual characteristic of interest under the study.

The weight is being measured in the winter season, when a person is likely to wear woolen garments, or other heavy garments to keep themselves warm. Moreover, the weighing machine is kept at the front of the store next to the checkout counter, where the impact of the season should evidently be strong, so that the person cannot be expected to take off their winter wear before weighing themselves. All these indicate that the weight of the person is likely to come out to be higher than their original weight, due to the extra layers of clothing. Hence, the measurements of the weight are likely to be biased.

Since the electronic machine is said to be sophisticated, it can be expected to give consistent measurements, and can hence be considered reliable.

A machine designed to measure weight cannot measure blood pressure; likewise, a machine designed to measure blood pressure cannot be used to measure weight. This indicates that a weighing machine must have been used to measure the weight, whereas a blood pressure gauge must have been used to measure the blood pressure. As a result, the measurements of weight and blood pressure are likely to be valid.