So that would be an unreliable but valid measure. Maybe I’m just not too bright, and so while her estimate of my intelligence fluctuates pretty wildly from day to day, it’s basically right. Similarly, while my mum’s estimate of my intelligence is a bit unreliable, she might be right. In technical terms, this is a reliable but invalid measurement. However, this highly reliable answer doesn’t match up to my true weight at all, therefore it’s wrong. If I’m holding a sack of potatos when I step on and off of the bathroom scales, the measurement will still be reliable: it will always give me the same answer. Notice that this concept of reliability is different to the question of whether the measurements are correct (the correctness of a measurement relates to it’s validity). Measuring my intelligence by means of “asking my mum” is very unreliable: some days she tells me I’m a bit thick, and other days she tells me I’m a complete moron. The measurement of my weight by means of a “bathroom scale” is very reliable: if I step on and off the scales over and over again, it’ll keep giving me the same answer. Reliability is actually a very simple concept: it refers to the repeatability or consistency of your measurement. In this section I’ll talk about reliability we’ll talk about validity in the next chapter. Put simply, the reliability of a measure tells you how precisely you are measuring something, whereas the validity of a measure tells you how accurate the measure is. At this point, we should start discussing the obvious question: is the measurement any good? We’ll do this in terms of two related ideas: reliability and validity. \)Īt this point we’ve thought a little bit about how to operationalise a theoretical construct and thereby create a psychological measure and we’ve seen that by applying psychological measures we end up with variables, which can come in many different types.
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