Birthdays

I am intriged. When I look at the birthdays of my friends & family there seems to be a statistical anomaly:-

• Jan 5th - CW & RA
• Jan 21st - Daughter & CW(2)
• Feb 21st - VD / Feb 22nd - EP
• April 1st - CW(3) & RF / April 3rd - DT
• April 16th AD & DM
• May 6th - DC / May 8th SB / May 12th - SB
• June 18th CC & CT
• Nov 1st - JF / Nov 3rd - EC
• Dec 20th - PS / Dec 24th JP

There are others in the same months in the clusters but  further apart. Spooky or what? Am I unconciously selecting astrological types? Or is it just coincidence? If so what is the probability? Maybe someone out there can suggest a solution.