Finding socially responsible investments is easier than ever before, but questions still remain around just what impact these investments are actually having.

A responsible fund may call itself a low-carbon exchange-traded fund , but how much carbon is it actually mitigating?

"The challenge for impact investors is it can be hard to understand what's actually going on in these responsible fund strategies," says Amy O'Brien, head of responsible investing at Nuveen in New York City.

Socially responsible investors may be surprised at how many low-carbon ETFs hold the FANG names – Facebook (ticker: FB ), Amazon ( AMZN ), Netflix ( NFLX ) and Google, now Alphabet ( GOOG , GOOGL ) – and other tech companies that have just bought carbon offsets to reduce their footprint, says New York-based Kellen Parker, vice president of Analytics at Flat World Partners.

Here are a few ways investors can assess whether they are making socially responsible investments.

Learn to measure socially responsible investments.

Mind the data gaps.

Understand the methodology behind the rating.

Work with a professional.

[See: 8 Ways to Build a Low-Cost Portfolio for Social Change .]

Learn to Measure Socially Responsible Investments

This was the story the team at nonprofit As You Sow uncovered when the organization started working with investors who wanted to divest fossil fuels.

"We found no one knew what they actually owned inside their mutual funds and there were a lot of false assumptions floating around," says Andrew Behar, the Oakland-based CEO of As You Sow. "We wanted to create tools that would enable transparency and allow investors to do their due diligence efficiently."

They created five free online tools that investors can use to screen their mutual funds against environmental, social and governance (ESG) issues. The five screening tools are for fossil-free funds, weapons-free funds, deforestation-free funds, tobacco-free funds and gender equality funds . Links to the tools can be found at As You Sow's website .

Each tool provides ESG data on the 5,000 most commonly held U.S. mutual funds and ETFs. Investors can search by fund name or ticker symbol or browse through the entire list.

The Forum for Sustainable and Responsible Investment (US SIF) provides a similar list of all sustainable, responsible and impact funds offered by US SIF member firms. The chart lists how a fund addresses 15 ESG criteria from climate to labor relations to animal welfare. You can also find information on some funds' proxy voting records and policies (also available in their N-PX report filed with the SEC), an issue that's becoming increasingly important to socially responsible investors.

Responsible investors want to know how managers are using the power of their proxy votes to influence companies, O'Brien says. But this activity is not yet picked up in responsible fund ratings.

Mind the Data Gaps

While free tools are a great place to begin your research, Amanda Agati, co-chief investment strategist at PNC Financial Services Group in Philadelphia, warns there's an element of "you get what you pay for."

"Just because you're scoring a portfolio doesn't mean the underlying data is sound, or that it meets your overall goals," she says.

With no standardized metric for measuring impact criteria, rankings are subjective at best.

ESG ratings aren't like bond ratings, Parker says. You'd be alarmed if Fitch and Moody's differed strongly on a company, but two of the biggest ESG ratings providers, MSCI and Sustainalytics, "can vary widely on a given name."

The problem is many ratings agencies rely on self-reporting from companies. Companies don't always disclose ESG data and when they do disclose, the information can be incomplete or vague.

"While law says anything that's financially material must be disclosed, there's still a limit to what companies put out there," Parker says. Firms are naturally inclined to disclose information that's beneficial to them and to not disclose that which is unfavorable. This puts ratings agencies in a tight spot.

You also run into the issue of what companies say versus what they do, Parker says. "Are (ratings agencies) assuming that just because a company says something, they actually police themselves?"

[See: 7 Socially Responsible ETFs for Investors of All Stripes .]

Understand the Methodology Behind the Rating

Firm ratings are more views than definitive rankings, says Parker, who adds investors shouldn't "just sandwich someone else's view onto your own without understanding what's going into it."

When using analyst opinions and socially responsible fund rankings to evaluate an impact investment, he says to look for ones that disclose where they're getting their data and how they're dealing with information gaps.

"How are they balancing what the company discloses, what analysts covering the company think and quantitative models estimating their impact?" he asks. You should be able to delve into their methodology, "especially what they're estimating and what they're not."

If all they provide is a numerical score, "I'd be skeptical," he says.

Work with a Professional

For many socially responsible investors, it comes back to where the road often leads: Finding someone with more resources and clout than you to help with the legwork.

"Professional portfolio managers and asset management firms can peer through the data and spend the time scrubbing" it to provide a more holistic and individualized analysis, Agati says.

Firms like Nuveen help investors quantify the impact of their responsible investments with impact reports. Each report lists the responsible fund's impact toward the U.N.'s 12 sustainability metrics. For instance, according to Nuveen's report, the TIAA-CREF Social Choice Bond Fund ( TSBIX ) financed projects and organizations, which provided more than 2 million affordable mortgages in 2017. It also financed projects and organizations that collectively avoided 77.5 million metric tons of carbon emissions, the equivalent of taking 16.6 million cars off the road for one year.

If socially responsible investing is important to you, tell your financial advisor .

"The client-advisor conversation is critical," O'Brien says. "Advisors need to hear from their clients that they're interested in (socially responsible investing), so they build out their practice management."

[See: 8 Questions to Ask During Volatile Markets .]

Ask and you shall receive: As more investors and their advisors ask for investments that are truly socially responsible, investment firms will respond by improving the transparency of their socially responsible investments. And with greater transparency comes greater accountability and ultimately greater impact.

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