Science, logic and the burden of proof

Wood alphabet in word null on artificial green grass background

Anyone who has read my blog or Facebook page for any length of time knows that I rarely censor comments. I am happy to argue with anyone, no matter how outrageous their claims, because there’s always a possibility I can convince readers, if not the commentor herself.

Like anyone trained in science, I argue using the principles of basic logic and scientific evidence. But it’s difficult, if not impossible, to argue with laypeople who might understand neither.

No one has to prove elephants can’t fly in order to claim they can’t fly.

It’s not difficult to prove them wrong. That’s easy. To anyone with a modicum of understanding of logic, they’ve made fools of themselves. But it’s difficult to get them to understand that they are wrong, or that they have not been able to support their own claims. What follows, therefore, is a very basic primer on the null hypothesis, the cornerstone of scientific reasoning.

Let’s start with the definition of a hypothesis:

a supposition or proposed explanation made on the basis of limited evidence as a starting point for further investigation.

Most people understand that a hypothesis is a provisional claim and it remains provisional until it can be tested and shown to be true.

It can be a description: Pigs are mammals.

It can be a prediction: Tadpoles become frogs.

It can be a claim of relationship: Light is necessary for plants to grow.

You can generate a hypothesis about nearly anything.

But what many laypeople don’t understand is that science ALWAYS starts with the null hypothesis.

What’s the null hypothesis?

The null hypothesis is that there is NO connection between the elements of any hypothesis.

For the hypotheses above, the null hypotheses are:

Pigs are not mammals.

Tadpoles and frogs are unrelated.

Light has nothing to do with the growth of plants.

The null hypothesis is NOT the negative of the hypothesis. This is where laypeople often get confused. It null hypothesis is ALWAYS the claim that there is no connection.

If you want to claim that pigs are mammals, you must prove they are mammals because the null hypothesis is that there is no connection between pigs and mammals. In other words the BURDEN OF PROOF is on the person who asserts the connection.

Laypeople usually understand this to a certain extent, but because they don’t understand the null hypothesis, they don’t understand who must offer proof.

If you claim pigs are mammals YOU must prove the assertion that pigs are mammals. If I claim pigs are not mammals, I DON’T have to prove it because I am merely stating the null hypothesis that there is no connection and the null hypothesis is ALWAYS true until someone proves it isn’t.

To better understand how this works, it is helpful to use an absurd example.

Suppose I say that elephants can fly. I assert that if you push an elephant off a cliff, it will flap its massive ears and settle safety to the ground.

If you insist that elephants can’t fly, do you have to prove that they can’t? Do you have to push an elephant off a cliff and watch it fall to its death below before you can claim that an elephant can’t fly?

No, because the null hypothesis is ALWAYS that there is NO CONNECTION between elephants and flight.

Here’s a real world example:

Yesterday I noted on my Facebook page that there is no evidence that immediate skin-to-skin contact is necessary for mother-infant bonding. I therefore claimed that skin-to-skin contact is not necessary for bonding.

The lactivists promptly swooped in.

Janet KS vehemently disagreed with me. I wrote:

Please supply scientific evidence that skin-to-skin has had any impact on child mental health at the population level.

She offered what she thought was a clever riposte:

Please supply scientific evidence that skin-to-skin has NOT had any impact on child mental health at the population level.

But all she did was demonstrate that she doesn’t understand how science works. The null hypothesis, the starting point for any claim, is ALWAYS that there is no connection, in this case, no connection between skin-to-skin and child mental health. It does not require proof; it is accepted as true.

The burden of proof is on those who want to assert that skin-to-skin improves child mental health. No one has to prove it doesn’t because the null hypothesis is not the negative of the hypothesis. It is the assumption that there is no connection.

The same thing applies to most of the major claims of contemporary lactivism. If lactivists want to claim that breastfeeding in industrialized countries saves lives, they have to show that it does.

It goes both ways.

If I want to claim that aggressive breastfeeding promotion leads to serious, life threatening neonatal complications, I have to prove that it does. Lactivists don’t have to prove that it doesn’t.

The bottom line is this: science ALWAYS starts with the assumption that there is no connection. If you want to claim otherwise, YOU have to prove otherwise.

  • KJA

    When I was teaching research methods to nursing students, my rationale for the use of the null hypothesis was, “in order to avoid the accusation that your research only proved what you wanted”.

    I conceptualize research decisions as an internal struggle between what the researcher WANTS (publications, a theory named after them, further research funding) and a researchers’ duty of care (to figure out what provides the best interventions for patients).

    As a researcher, I need to ensure that what I WANT does not take precedence over my duty of care to current and future patients. One of the best tools to offer this protection is the null hypothesis.

  • Mel

    I got to hold Spawn skin-to-skin for the first time when he was 7 days old. That was pretty fast since my parents had to wait 15 days to hold my sister and I.

    Spawn’s been diagnosed with cerebral palsy and anxiety; so have I and my identical twin sister.

    I’ve always chalked his diagnoses up to 1) extreme prematurity leading to BPD and 2) genetics since CP seems to be the way our brains respond to hypoxia.

    I cannot with a straight face make an argument that any of the three of us would have been better off if we had been tossed onto the bare chest of our respective mothers prior to stabilization.

    Actually, that probably would have killed my twin sister even after she was stabilized.

    Spawn would have just been insulted because we were prioritizing skin-to-skin over filing a legal suit over his illegal forced eviction. (The suit reached a settlement where Spawn was given a larger apartment with better views and more fun toys.)

    • KeeperOfTheBooks

      Your Spawn stories still make me smile. 🙂

      • Mel

        He is an excellent addition to our family! Even on rough days, he’s a little burst of sunshine in our lives. I’m never going to look at heavy equipment the same way after seeing how excited Spawn gets every time he sees anything with wheels – the bigger the better.

        • KeeperOfTheBooks

          Heh. Baby Books 2 started his truck phase just a) as he started saying vaguely-recognizeable words and b) when we embarked on a cross-country drive to my parents’-in-laws’ house. He would squeal/shriek “truck!!!” at the top of his voice, which would have been a good deal less awkward if he said his “t”s a bit less like “f”s at the time…

    • demodocus

      What?! Your kidneys and bladder weren’t good enough?? 😉

      • Mel

        Oh, Spawn loved a good bladder kicking session at 3 am – but the sheer number of tubes and wires that he had in his reach in the isolette were an great upgrade. That’s not including the entire cacophony of alarms he learned to set off. He had a NICU buddy that we’ll call Ace. Spawn and Ace were both placed on NIPPV or CPAP within a few hours of each other. Within less than 24 hours, each boy had learned that exhaling as hard as they could through their nose would set off a transient “high reverse flow” alarm for a few seconds. And that’s when the “Bat Boy” auditory signaling between the two began. Spawn would set off his alarm and within a second Ace would set off his alarm. Next, Ace would set off his alarm and Spawn would match him. It was funny for the first 10 times or so – but the nurses were really over it by the end of the first 24 hours of alarm after alarm after alarm from the duo.

        Even after Spawn and Ace was upgraded to a type of CPAP that didn’t have a reverse flow alarm (and that happened REALLY fast so the nurses didn’t lose their minds) – and even later when he was on a nasal cannula – he’d think for a second, blow air out his nose really hard, then pause and wait to see if the alarms would go off.

        • demodocus

          Well, he didn’t _know_ such fun existed outside 😉

          Seriously, that kid is quite the problem solver.

  • Anna

    Janet is capable of understanding but doesn’t want to. Jamie isn’t capable of understanding. I’d feel bad for her if shes wasn’t so damn aggressive.

  • fiftyfifty1

    But but but…I *insist* that you prove that elephants can’t fly by pushing one off a cliff (and then when it doesn’t fly I will insist you try a different elephant, because probably you pushed the first one wrong or something.)

    • Mel

      *watches elephant fall through the air*

      You totally put spin on Dumbo and elephants can’t fly if they have any longitudinal spin on them. Let’s try again with Daisy – but no spin this time!

      • MaineJen

        We could try lateral spin, like with a football…*pictures elephant spinning with trunk and ears whirling like a pinwheel* However, that would require a catapult.

    • AnnaPDE

      Well of course they can’t fly off cliffs. That’s just not their natural way of flying.
      Elephants fly _just fine_ when put into a cargo plane, as nature intended.

      • KeeperOfTheBooks

        This made me actually laugh out loud.

  • Side note: same goes for claims of deities, magic, faeries, chakras, healing crystals, etc. The person making the claim involving the supernatural gets to back up that claim with evidence; the atheist position is the null hypothesis and does not require evidence to support it.