Indoor air pollution resulting from the use of solid fuels [by poorer segments of society] is a major killer. It claims the lives of 1.5 million people each year, more than half of them below the age of five: that is 4000 deaths a day. To put this number in context, it exceeds total deaths from malaria and rivals the number of deaths from tuberculosis.Source 15
My returns are based on full cash purchase of the properties, as it is hard to compare the attractiveness of properties at different price ranges when only calculating down payment or properties that need very little rehab/updates. I did think about the scores assigned to each factor, but I believe tax deductions are a SIGNIFICANT factor when comparing passive income steams.

Another way to generate passive income is to invest and be a silent partner in a business. This is very risky, but with risk comes the potential for high returns. For example, several years ago both Lyft and Uber were looking for private investors to invest in their companies. Today, they are worth billions - but you as an investor would only reap that benefit if they go public via an IPO, or get acquired. So, it's risky.

3. Start as soon as possible. Building a livable passive-income stream takes a tremendously long time, largely because of declining interest rates since the late 1980s. Gone are the days of making a 5%-plus return on a short-term CD or savings account. Today, the best 12-month CD is at 2.5%, and the best money-market rate is about 1.85%, which is not bad, considering such rates were below 0.5% just a couple of years ago. Know that every $100 you save can generate at least $2.5 in passive income.

These days, low-risk bond yields aren’t enough to meet most income needs. When investing in bonds, the income typically comes as coupon payments – contractually guaranteed interest payments at predictable intervals.  There are many kinds of bond income available, so you must strike a balance between reaching for higher income (yield) and limiting risk.