Exclusionary screening, also known as negative screening, is a responsible investment strategy where certain companies, sectors, or practices are excluded from an investment portfolio based on specific ethical guidelines or criteria. It is widely regarded as the oldest and simplest approach within the realm of responsible and sustainable investing.

1. Oldest and Simplest Approach: Exclusionary screening is indeed the oldest and simplest approach within responsible investment. This method has been used for decades, with early examples including the exclusion of companies involved in controversial activities such as tobacco, alcohol, or weapons production. The simplicity of this approach lies in its straightforward criteria: if a company or sector falls within the excluded category, it is not considered for investment.

2. Reducing Portfolio Tracking Error and Active Share: Contrary to option A, exclusionary screening does not necessarily reduce portfolio tracking error and active share. In fact, it can increase tracking error and active share by deviating from the benchmark index. This is because excluding certain companies or sectors means that the portfolio may differ significantly from the benchmark, potentially increasing both tracking error and active share.

3. ESG Rating Methodology: Option C describes a different approach known as positive or best-in-class screening, where a given ESG rating methodology is employed to identify and invest in companies with better ESG performance relative to their industry peers. This is distinct from exclusionary screening, which is based on predefined ethical or moral criteria rather than relative ESG performance.

References from CFA ESG Investing:

Exclusionary Screening: The CFA Institute describes exclusionary screening as the process of excluding certain sectors, companies, or practices from a portfolio based on specific ethical, moral, or religious criteria. This method has historical roots and is considered the simplest and most traditional form of responsible investment.

Positive/Best-in-Class Screening: The CFA curriculum differentiates exclusionary screening from positive screening, where investments are made in companies with superior ESG performance within their sectors, using ESG rating methodologies to guide the selection process.

In conclusion, exclusionary screening is correctly identified as the oldest and simplest approach within responsible investment, making option B the verified answer.

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