The Sad Story of Fish Oil and Small Sample Sizes

Fight disinformation: Sign up for the free Mother Jones Daily newsletter and follow the news that matters.


Keith Humphreys passes along the sad story today of fish oil’s journey from miracle cure to nothingburger. The chart below shows the evolution of research on Omega-3 supplements over the past 17 years, where a small “relative risk” number indicates a beneficial effect and 1.0 indicates no effect at all:

Humphreys explains how this happens:

When there were only a little data available, fish oil looked like manna from heaven. But with new studies and more data, the beneficial effect has shrunk to almost nothing. The current best estimate of relative risk (bottom row of table) is 0.96, barely below 1.0. And the “confidence interval” (the range of numbers in parentheses), which is an indicator of how reliable the current estimate is, actually runs to a value slightly greater than 1.0.

Why does this happen? Small studies do a poor job of reliably estimating the effects of medical interventions. For a small study (such as Sacks’ and Leng’s early work in the top two rows of the table) to get published, it needs to show a big effect — no one is interested in a small study that found nothing. It is likely that many other small studies of fish oil pills were conducted at the same time of Sacks’ and Leng’s, found no benefit and were therefore not published. But by the play of chance, it was only a matter of time before a small study found what looked like a big enough effect to warrant publication in a journal editor’s eyes.

Caveat lector. Don’t believe everything you read, especially if there’s only one study and it has a small sample size. It’s still possible that fish oil has a slight beneficial effect, but it’s unlikely. Spend your money on something else.

WE CAME UP SHORT.

We just wrapped up a shorter-than-normal, urgent-as-ever fundraising drive and we came up about $45,000 short of our $300,000 goal.

That means we're going to have upwards of $350,000, maybe more, to raise in online donations between now and June 30, when our fiscal year ends and we have to get to break-even. And even though there's zero cushion to miss the mark, we won't be all that in your face about our fundraising again until June.

So we urgently need this specific ask, what you're reading right now, to start bringing in more donations than it ever has. The reality, for these next few months and next few years, is that we have to start finding ways to grow our online supporter base in a big way—and we're optimistic we can keep making real headway by being real with you about this.

Because the bottom line: Corporations and powerful people with deep pockets will never sustain the type of journalism Mother Jones exists to do. The only investors who won’t let independent, investigative journalism down are the people who actually care about its future—you.

And we hope you might consider pitching in before moving on to whatever it is you're about to do next. We really need to see if we'll be able to raise more with this real estate on a daily basis than we have been, so we're hoping to see a promising start.

payment methods

WE CAME UP SHORT.

We just wrapped up a shorter-than-normal, urgent-as-ever fundraising drive and we came up about $45,000 short of our $300,000 goal.

That means we're going to have upwards of $350,000, maybe more, to raise in online donations between now and June 30, when our fiscal year ends and we have to get to break-even. And even though there's zero cushion to miss the mark, we won't be all that in your face about our fundraising again until June.

So we urgently need this specific ask, what you're reading right now, to start bringing in more donations than it ever has. The reality, for these next few months and next few years, is that we have to start finding ways to grow our online supporter base in a big way—and we're optimistic we can keep making real headway by being real with you about this.

Because the bottom line: Corporations and powerful people with deep pockets will never sustain the type of journalism Mother Jones exists to do. The only investors who won’t let independent, investigative journalism down are the people who actually care about its future—you.

And we hope you might consider pitching in before moving on to whatever it is you're about to do next. We really need to see if we'll be able to raise more with this real estate on a daily basis than we have been, so we're hoping to see a promising start.

payment methods

We Recommend

Latest

Sign up for our free newsletter

Subscribe to the Mother Jones Daily to have our top stories delivered directly to your inbox.

Get our award-winning magazine

Save big on a full year of investigations, ideas, and insights.

Subscribe

Support our journalism

Help Mother Jones' reporters dig deep with a tax-deductible donation.

Donate