Assumption #1: The response (e.g., judgement) that is made by your two raters is measured on a nominal scale (i.e., either an ordinal or nominal variable) and the categories need to be mutually exclusive.Therefore, in order to run a Cohen's kappa, you need to check that your study design meets the following five assumptions: If these assumptions are not met, you cannot use Cohen's kappa, but may be able to use another statistical test instead. SPSS Statistics AssumptionsĬohen's kappa has five assumptions that must be met. However, before we introduce you to this procedure, you need to understand the different assumptions that your data must meet in order for Cohen's kappa to give you a valid result. This "quick start" guide shows you how to carry out Cohen's kappa using SPSS Statistics, as well as interpret and report the results from this test. Note: There are variations of Cohen's kappa (κ) that are specifically designed for ordinal variables (called weighted kappa, κ w) and for multiple raters (i.e., more than two raters). This is something that you have to take into account when reporting your findings, but it cannot be measured using Cohen's kappa (when comparing two the doctors). However, it is worth noting that even if two raters strongly agree, this does not necessarily mean that their decision is correct (e.g., both doctors could be misdiagnosing the patients, perhaps referring them too often when it is not necessary). Since the results showed a very good strength of agreement between the two doctors, the head of the local medical practice feels somewhat confident that both doctors are diagnosing patients in a similar manner.
The level of agreement between the two doctors for each patient is analysed using Cohen's kappa. Both doctors look at the moles of 30 patients and decide whether to "refer" or "not refer" the patient to a specialist (i.e., where "refer" and "not refer" are two categories of a nominal variable, "referral decision"). For example, the head of a local medical practice might want to determine whether two experienced doctors at the practice agree on when to send a patient to get a mole checked by a specialist. There are many occasions when you need to determine the agreement between two raters. Cohen's kappa (κ) is such a measure of inter-rater agreement for categorical scales when there are two raters (where κ is the lower-case Greek letter 'kappa'). In research designs where you have two or more raters (also known as "judges" or "observers") who are responsible for measuring a variable on a categorical scale, it is important to determine whether such raters agree. Cohen's kappa using SPSS Statistics Introduction
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