Can I change the size of UIActivityIndicator?

The following will create an activity indicator 15px wide:

#import <QuartzCore/QuartzCore.h>

...

UIActivityIndicatorView *activityIndicator = [[[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray] autorelease];
activityIndicator.transform = CGAffineTransformMakeScale(0.75, 0.75);
[self addSubview:activityIndicator];

While I understand the sentiment of TechZen’s answer, I don’t think adjusting the size of a UIActivityIndicator by a relatively small amount is really a violation of Apple’s standardized interface idioms – whether an activity indicator is 20px or 15px won’t change a user’s interpretation of what’s going on.