Cronbach's Alpha

Dear all,

I have 12 companies and I am developing a scale for innovation. I want to
check the reliability of my scale. I delivered it to different (engineers,
managers etc) people in each company and an unequal number of values.
For example:
Company 1    2 engineers      2 managers
Company 2    4 engineers     10 managers
etc.

My question is can I use 'ordinary Cronbach's alpha or do I need a modified
weighted cronbach's alpha. If so, does such a thing exist in R?

Thanks,
Jim.

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