Do some months really give better returns compared to others?

I was asked by a friend to find out if it true that equities perform better in certain months compared to others.

I have done a some analysis on monthly return on Sensex since its inception in April 1979. To my surprise I made the following observation

• February, June, July, September and December are the best months to buy Equity.
• The median return during these months are 2.4%, 1.8%, 2.5%,4.4nd 4.6% respectively
• The ratio of positive months to total months have been 0.58, 0.66 , 0.66, 0.61, 0.81
• The ratio indicates that out of 32 Months since 1979 58% of the time the returns on index were positive in February.
• Lets look at the data form December it says that 81% of the time December gave positive returns and on the top of that the median returns in the month of December has been to the tune of 4.6%
• Similarly October and March are the worst months to buy Equity
• The Median return during the month of march are -2.6% and -1.3% during October.
• The ratio of positive months in march and October is 35%.
• The other worst month to buy or hold equity are January  and August
• While April, May and November remains inconclusive.

I must also add that the statistical validity of the observation can not be tested as the number of observations are very low.  While negative returns in March may be due to ending month of the year where investors book profit or due to the effect of Union budget. the effect of other months cant be explained.