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Participants (N=14) filled in two questionnaires at two points of time, and I want to see the correlation between the variables.

Is this sample size sufficient?

Also, should I have reverse coded the items before running the correlation analysis?

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Are you interested in the correlation between each variables/items or a composite score (e.g., sum or mean score) derived from them? – chl♦ Oct 16 '12 at 21:46
I'm looking at the correlation between each item. – Julie Oct 16 '12 at 21:52
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"Is this sample size sufficient?" ... sufficient to do what, exactly? You can compute correlations with fewer data points. And why would you reverse-code anything? – Glen_b Oct 16 '12 at 21:54
Then reverse scoring doesn't matter, but we'll probably want to know how many items you have. – chl♦ Oct 16 '12 at 21:54
I meant is the sample size sufficient for correlation analysis? – Julie Oct 16 '12 at 21:59
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Correlations are valid with fewer than 14 points, but they become more accurate with more data. Exactly how much more accurate depends on various things, but if the data are bivariate normal, the standard error is approximately

$SE(r) = \frac{(1-\rho^2)}{\sqrt{n-1}}$

However, with 16 items, the data clearly aren't going to be exactly bivariate normal. Still the denominator term should give you a rough idea: Accuracy goes up as the square root of N; with 4 times as many subjects, it's twice as accurate. And it's more accurate the higher the population correlation.

There is no reason to reverse code, that will just change the sign of the correlation.

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Thank you so much! – Julie Oct 18 '12 at 1:56

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