Nav: Home

Groundwater studies can be tainted by 'survivor bias'

September 05, 2019

Bad wells tend to get excluded from studies on groundwater levels, a problem that could skew results everywhere monitoring is used to decide government policies and spending.

Researchers at the University of Waterloo uncovered the problem while examining a discrepancy between scientific data and anecdotal evidence in southern India.

Reports on thousands of wells and satellite images taken between 1996 and 2016 suggested groundwater levels were rising, good news in an area where it is vitally important for agriculture.

At the same time, however, fieldworkers were hearing more stories from farmers about wells running dry, suggesting levels were actually declining.

Researchers solved the apparent paradox by first obtaining census data that backed up the anecdotal evidence. It showed, for example, that more farmers were digging expensive deep wells in the hard-rock aquifer.

"If indeed groundwater levels are going up, why would farmers choose to pay more and dig deeper wells?" asked Nandita Basu, a civil and environmental engineering professor. "It didn't make sense."

Researchers then examined the well data and found that those with missing water level data were often excluded from analysis because they were considered unreliable.

When the excluded wells were added back into the mix, the results confirmed the evidence from farmers that groundwater levels were decreasing, not increasing.

"They were systematically picking the wells with a lot of data and potentially ignoring the wells that were going dry because they had incomplete data," said Tejasvi Hora, an engineering PhD student who led the research.

The culprit was identified as something called 'survivor bias,' a statistical phenomenon that results in the exclusion of negative data.

When wells ran dry, there were no water levels to report. That created gaps in reports for those wells, and their incomplete data was then discarded as inferior to the complete data from good wells that hadn't run dry.

Basu, also a professor of earth and environmental sciences and a member of the Water Institute at Waterloo, said the lesson from southern India is applicable anywhere in the world that groundwater levels are monitored and analyzed.

"Our main point is that bad data is good data," she said. "When you have wells with a lot of missing data points, that is telling you something important. Take notice of it."

"Whenever you're focusing only on complete data, you should take a step back and ask if there is a reason for the incomplete data, a systematic bias in your data source," Hora said.
-end-
Basu and Hora collaborated with Veena Srinivasan, a researcher at an environmental think tank in India.

A paper on their work, The Groundwater Recovery Paradox in South India, appears in the journal Geophysical Research Letters.

University of Waterloo

Related Data Articles:

Data centers use less energy than you think
Using the most detailed model to date of global data center energy use, researchers found that massive efficiency gains by data centers have kept energy use roughly flat over the past decade.
Storing data in music
Researchers at ETH Zurich have developed a technique for embedding data in music and transmitting it to a smartphone.
Life data economics: calling for new models to assess the value of human data
After the collapse of the blockchain bubble a number of research organisations are developing platforms to enable individual ownership of life data and establish the data valuation and pricing models.
Geoscience data group urges all scientific disciplines to make data open and accessible
Institutions, science funders, data repositories, publishers, researchers and scientific societies from all scientific disciplines must work together to ensure all scientific data are easy to find, access and use, according to a new commentary in Nature by members of the Enabling FAIR Data Steering Committee.
Democratizing data science
MIT researchers are hoping to advance the democratization of data science with a new tool for nonstatisticians that automatically generates models for analyzing raw data.
Getting the most out of atmospheric data analysis
An international team including researchers from Kanazawa University used a new approach to analyze an atmospheric data set spanning 18 years for the investigation of new-particle formation.
Ecologists ask: Should we be more transparent with data?
In a new Ecological Applications article, authors Stephen M. Powers and Stephanie E.
Should you share data of threatened species?
Scientists and conservationists have continually called for location data to be turned off in wildlife photos and publications to help preserve species but new research suggests there could be more to be gained by sharing a rare find, rather than obscuring it, in certain circumstances.
Futuristic data storage
The development of high-density data storage devices requires the highest possible density of elements in an array made up of individual nanomagnets.
Making data matter
The advent of 3-D printing has made it possible to take imaging data and print it into physical representations, but the process of doing so has been prohibitively time-intensive and costly.
More Data News and Data Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Listen Again: Meditations on Loneliness
Original broadcast date: April 24, 2020. We're a social species now living in isolation. But loneliness was a problem well before this era of social distancing. This hour, TED speakers explore how we can live and make peace with loneliness. Guests on the show include author and illustrator Jonny Sun, psychologist Susan Pinker, architect Grace Kim, and writer Suleika Jaouad.
Now Playing: Science for the People

#565 The Great Wide Indoors
We're all spending a bit more time indoors this summer than we probably figured. But did you ever stop to think about why the places we live and work as designed the way they are? And how they could be designed better? We're talking with Emily Anthes about her new book "The Great Indoors: The Surprising Science of how Buildings Shape our Behavior, Health and Happiness".
Now Playing: Radiolab

The Third. A TED Talk.
Jad gives a TED talk about his life as a journalist and how Radiolab has evolved over the years. Here's how TED described it:How do you end a story? Host of Radiolab Jad Abumrad tells how his search for an answer led him home to the mountains of Tennessee, where he met an unexpected teacher: Dolly Parton.Jad Nicholas Abumrad is a Lebanese-American radio host, composer and producer. He is the founder of the syndicated public radio program Radiolab, which is broadcast on over 600 radio stations nationwide and is downloaded more than 120 million times a year as a podcast. He also created More Perfect, a podcast that tells the stories behind the Supreme Court's most famous decisions. And most recently, Dolly Parton's America, a nine-episode podcast exploring the life and times of the iconic country music star. Abumrad has received three Peabody Awards and was named a MacArthur Fellow in 2011.