<DIV>Dear all,</DIV> <DIV>I have a basic question on the Rasch model.</DIV> <DIV>We always hear that Rasch measures are linear while raw scores aren't. Linearity is defined as "equal increments to the difficulty or ability measures when one more unit is added to a person's or an item's location".</DIV> <DIV>What I can't grasp is why Rasch measures are linear? What's magic about the Rasch measures. Once I heard "Rasch measures are cnstructed to be linear". But how?</DIV> <DIV>I'd be grateful if someone explains in laymen terms that why Rasch measures are linear.</DIV> <DIV>Regards</DIV> <DIV>Anthony</DIV><p>
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