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Scientific Measures: Reliability and Validity

Measurement is an important part of the scientific process. The key aspects concerning the quality of scientific measures are reliability and validity.     

Reliability is a measure of the internal consistency and stability of a measuring device.

Validity gives us an indication of whether the measuring device measures what it claims to. 

Internal consistency is the degree in which the items or questions on the measure consistently assess the same construct.  Each question should be aimed at measuring the same thing.  Internal consistency is often measured using Cronbach’s Alpha — a super-correlation of all the items on the scale. If the score is .70 or higher the measurement is acceptable.  However, .80 or higher is preferable.  It is also important to consider the context when considering the score that reflects internal consistency.   

3 Comments to
Scientific Measures: Reliability and Validity

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  1. Thanks for this Jamie. The sad part is that many claims in neurological, sociological, and psychological circles simply do not stand up to the scientific method. Yet there isn’t a social abnormality that one can’t find the sentence that “Scientist believe it is combination of genetic and environmental factors.” While often times the environmental factors show enough consistency that genetic factors do not. There is no fat, gay, alcoholic, sociopath, addiction, or the like gene. We have not proven what “chemically balanced” means to even begin to established what chemically imbalanced means. We do all this research, write all these books, immortalize the people who go on to prove these theories about our own control and the importance of upbringing, then we reject it out of hand when it comes to making policies and passing on information.

    One thing that seems simple but always confuses me when reading a study is what stipulates “double blind”. can you elaborate on that? Thanks for this.

  2. A blind study is when the participant is not informed of information that could possibly create a bias in their perception e.g. whether a pill in a drug test is placebo or the actual drug. But the experimenter does know.

    In a double blind study, both the participant and the experimenter do not know who is in the control group and who is in the experimental group, to prevent the experimenter unwittingly creating bias.
    e.g. in a drug trial, the participant and the experimenter do not know who is receiving the placebo or the drug.

    Hope I explained that well enough!




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