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We collected data on a 7-point survey and it should have been on a 9-point scale. How do you convert a 7-point scale to a 9-point scale?

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    $\begingroup$ I would say that the general answer is "you don't". But why do you say it "should" have been collected on a 9 point scale? Are you are trying to compare it to other data that was collected using a 9 point scale? Or are you attempting to merge it with other data? Or something else? $\endgroup$
    – Peter Flom
    Dec 18 '19 at 14:34
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You should not convert individual answers.


However, if you want to compare your work in the 7 point scale with a different work on a 9 point scale, you can make a linear transform of the type: $$ y = \frac{x-m}{a} $$ where $x$ is the mean or the median in the 7 point scale, $m$ is the minimum of that scale, $m=1$ in your case, and $a$ is the amplitude of the scale, in that case it will be $a = 7 - 1 = 6$. For the 9 point scale, the transformation formula is the same, but $a = 9 - 1 = 8$. Note that the standard deviation and the variance will each have their own transformations.

The transformed value will be in the interval $[0; 1]$ and you may find that, for instance, $4.2$ in the 7 point scale corresponds to a higher value than $4.8$ in the 9 point scale.

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  • $\begingroup$ Sorry, I meant to comment on the original post. I will delete my comment on your answer $\endgroup$
    – Peter Flom
    Dec 19 '19 at 11:25
  • $\begingroup$ OK. No worries. $\endgroup$ Dec 19 '19 at 11:44

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