1) Why some companies in India employ jonit auditors (excluding the national banks that are required by regulation)? Where can I get some official documentation on this phenomenon?
2)Comparing BSE and NSE, which is the more important stock exchange in India?
Can we say that the quality of the listed companies in BSE are generally better than the ones listed in NSE?
If I want to choose a sample body for my research for Indian listed companies, may I say BSE is a better choice than NSE?
There is no specific phenomenon on appointment of such joint auditors by the companies. Its a general thing noticed that one of the joint auditor is some Big 4 MNC and another is some local firm. There is no phenomenon or any law in this regard. However, there is a logic behind it. Generally the other local firm is the one which is the auditor of the company since its inception and generally it happens that companies don't change their old auditors. Further, as the operations of the company grow to a large extent, they require experts as auditors and as mentioned that old auditors are not changed generally, they appoint MNC Audit Firm as Auditor jointly with their old auditors. This is purely a logic.
Considering BSE and NSE, NSE is more important stock exchange in India as it account for almost 90% of the Volume in the Stock Market. There is no difference as such in the quality of the companies listed on either of the stock exchanges. The difference is in the trading volumes of the shares that are dealt with the stock exchange. If you want to chose a sample for research in Indian Stock Market, then its better to go from a sample from NSE as the data on NSE most appropriately resembles the population rather than on BSE.