Correlation — Markets Kaise Milke Chalte Hain?

Correlation coefficient minus 1 se plus 1 ke beech hota hai. Plus 1 matlab perfect positive correlation, dono assets exactly same direction mein same magnitude pe move karte hain. Minus 1 matlab perfect negative correlation, ek upar jaata hai toh doosra exactly neeche aata hai. Zero matlab koi linear relationship nahi.

Practically koi bhi real asset pairs plus 1 ya minus 1 pe nahi hote. Lekin approximate correlations hain jo useful hain. Large cap Indian stocks generally NIFTY ke saath high positive correlation mein hote hain. Gold aur equity historically low to mildly negative correlation dikhate hain. Long-term government bonds aur equity generally negative correlation mein hote hain.

Correlation Pearson's formula se calculate hota hai: r = Covariance(X,Y) / [Standard Deviation(X) multiplied by Standard Deviation(Y)]. Yeh formula essentially normalize karta hai covariance ko dono assets ki individual volatilities se.

Portfolio variance ka formula hai: Portfolio Variance = Weight1 squared multiplied by Variance1 plus Weight2 squared multiplied by Variance2 plus 2 multiplied by Weight1 multiplied by Weight2 multiplied by Correlation multiplied by SD1 multiplied by SD2.

Is formula mein last term correlation pe depend karta hai. Agar correlation 1 ho, toh koi diversification benefit nahi milta. Agar correlation minus 1 ho, toh theoretically zero portfolio variance possible hai. Agar correlation zero ho, toh partial diversification milti hai.

Yahi reason hai ki portfolio mein ek hi sector ke bahut saare stocks rakhna true diversification nahi hai. IT sector ke 10 stocks ka correlation ek doosre ke saath bahut high hoga. Better approach hai different sectors, different asset classes, aur different geographies mein invest karna.

Correlation stable nahi rehta. Yeh time ke saath change hota rehta hai aur market conditions ke saath dramatically shift ho sakta hai. Normal times mein jo assets low correlation dikhate hain woh market crashes mein suddenly high correlation show karne lagte hain.

March 2020 mein COVID crash ke dauran, almost every asset class globally gira. Gold, equity, real estate, bonds, sab ek saath neeche gaye kuch days mein. Normally yeh sab different correlations mein move karte hain.

Is phenomenon ko correlation breakdown ya correlation instability kehte hain. Iska matlab hai ki historically low correlation ka matlab yeh nahi ki future mein especially during stress periods, same low correlation rahegi. Quant models jo static correlations assume karte hain woh market crises mein often fail karte hain.