January 18, 2019

What can Science do?

Plan for Today

1) Recap: Normative vs. Empirical claims

2) Empirical Claims: causal vs. descriptive

3) Falsifiable/Unfalsifiable

Recap

Normative vs. Empirical Claims

empirical claim:

is a claim about what is exists or what relationships occur between things that exist for which the basis consists of observation of the world and no value judgment about what is desirable.

  • in principle, we can fundamentally disagree on values but accept the same empirical claims

normative claim:

is a claim about what is desirable or undesirable or a claim about what action should be taken for which the basis assumes a value judgment about what is desirable/undesirable.

  • even if we accept same evidence is true, we won't accept the same normative claims if our (relevant) values differ

Normative Claims

Two varieties:

value judgments: a normative claim that directly states what goal or ideal is "right" or provides rules for judging which things are better or worse.

prescriptive claims: a normative claim that asserts (prescribes) what actions should be taken on the basis of both observation of the world and some assumed value judgment.

Normative vs. Empirical Claims

Empirical claims: can be evaluated using science

Normative claims: cannot (fully) be evaluated using science

Illustration

You and your friend win a sum of money in a lottery

You and your friend agree:

the most important ethical goal is minimizing human suffering. (value judgment)

You disagree on what to do:

  1. We should donate mosquito nets to stop malaria (prescriptive claim)

  2. We should give money directly to impoverished people (prescriptive claim)

Can science resolve the problem?

Illustration

Scientific Evidence

  • Malaria kills ~500k per year
  • Half of global population possibly exposed
  • Mosquito nets reduce likelihood of exposure
  • For each 100 to 1000 nets, 1 death prevented
  • Cost of mosquito nets is low
  • Cash transfers are expensive, effects on mortality mixed
  • Sums must be very large to affect mortality

What should you do?

Malaria nets!

Illustration

BUT…

What if you value minimizing suffering, but your friend values maximizing individual autonomy? (different value judgments)

Does the scientific evidence resolve your dispute?

  • NO! For prescriptive claims, science can only address how we get to our desired outcome, not which value judgment is right.

Illustration (Summary)

"Mosquito nets (A) prevent malaria (B)"

  • "A causes B" \(\not\to\) "we should do A"

  • Depends on how we value B

Does scientific evidence ever help?

Varieties of Empirical Claims

Some empirical questions:

  • How many firearms homicides (per capita) took place in the U.S. and Canada in 2016?

  • Why does the U.S. have more firearms homicides per capita than Canada?

  • How many refugees entered Germany during the migration wave of 2015?

  • Has the influx of refugees in Germany produced an increase in violent crime?

  • What percentage of Canadians use cannabis recreationally?

  • Has legalizing cannabis resulted in higher rates of impaired driving?

Some empirical claims

  • In 2017, Canada had 0.72 firearms homicides per 100K while the US had 3.37 per 100K.

  • The US has more firearms homicides per capita than Canada because the US has laxer gun laws.

  • Germany saw about 1.1 million refugees enter during 2015.

  • The AfD says: "Knife migration" has led to a dramatic increase in violent crime.

  • About 16% of Canadians over the age of 15 use cannabis.

  • There has been no increase in impaired driving after cannabis legalization

Descriptive claims:

descriptive claims:

claims about what exists (or has existed/will exist) in the world:

  • what phenomena exist (what kinds of things exist?)
  • what is the type of a specific phenomenon (what is this thing?)
  • amount/frequency of phenomena (how much of something is there?)
  • relative amount/frequency of phenomena across different places/times (how much of something is there here vs. there/now vs. then?)
  • what patterns are there in the shared appearance/non-appearance of different phenomena (does this thing usually appear together with that other thing?)

Which of these are descriptive? why?

  • In 2017, Canada had 0.72 firearms homicides per 100K while the US had 3.37 per 100K.

  • The US has more firearms homicides per capita than Canada because the US has laxer gun laws.

  • Germany saw about 1.1 million refugees enter during 2015.

  • The AfD says: "Knife migration" has led to a dramatic increase in violent crime.

  • About 16% of Canadians over the age of 15 use cannabis.

  • There has been no increase in impaired driving after cannabis legalization

Which of these are descriptive? why?

  • In 2017, Canada had 0.72 firearms homicides per 100K while the US had 3.37 per 100K. (descriptive)

  • The US has more firearms homicides per capita than Canada because the US has laxer gun laws.

  • Germany saw about 1.1 million refugees enter during 2015. (descriptive)

  • The AfD says: "Knife migration" has led to a dramatic increase in violent crime.

  • About 16% of Canadians over the age of 15 use cannabis. (descriptive)

  • There has been no increase in impaired driving after cannabis legalization (descriptive)

Causal claims:

causal claims:

are claims about the how one phenomena (\(X\)) affects or causes another phenomena (\(Y\)). Causal claims state that \(X\) acts on \(Y\) in some way, not merely that they appear together in some pattern:

  • the effect that one thing or event has on another thing (effects of causes)
  • the cause of some event or thing in the world (causes of effects)
  • the conditions under which some thing or event happens (causes of effects)
  • the process through which one thing affects another (causes of effects)

How to recognize causal claims

(compared to descriptive claims)

Causal claims include some kind of causal verb (or phrase). E.g.:

  • (non-exhaustive list): "causes", "influences","makes happen", "increases", "decreases", "results in", "was necessary for", etc.
  • can always be restated as a phrase with a verb, subject, and some object, where subject is the cause and object (or one of the objects) is the affected thing.
  • can always be restated as a phrase like "\(X\) causes \(Y\) to change in some way" or "\(Y\) changes in some way because of \(X\)"

Are these causal claims/questions?

  • There has been no increase in impaired driving after cannabis legalization

  • The city of Chicago has relatively-strict gun laws and a relatively-high gun-related murder rate.

  • Has legalizing cannabis resulted in higher rates of impaired driving?

  • Countries with more women in the legislature have more protections for womens' reproductive and marital rights.

How to recognize causal claims

(compared to descriptive claims)

Causal claims always imply: if we could directly manipulate one thing \(X\), then we would see \(Y\) change

Are these causal claims/questions?

  • There has been no increase in impaired driving after cannabis legalization

  • The city of Chicago has relatively-strict gun laws and a relatively-high gun-related murder rate.

  • Has legalizing cannabis resulted in higher rates of impaired driving?

  • Countries with more women in the legislature have more protections for womens' reproductive and marital rights.

Turned into causal claims:

  • Cannabis legalization did not increase impaired driving rates.

  • The city of Chicago's gun laws have not reduced the gun-related murder rate.

  • The entry of more women into a legislature results in more legal protections for womens' reproductive and marital rights.

Causal claims and Prescriptive Claims

You and your friend win a sum of money in a lottery

You and your friend agree:

the most important ethical goal is minimizing human suffering. (value judgment)

You disagree on what to do:

  1. We should donate mosquito nets to stop malaria (prescriptive claim)

  2. We should give money directly to impoverished people (prescriptive claim)

Causal claims and Prescriptive Claims

  • Assuming less malaria is good, resources are finite
  • What if mosquite nets don't prevent malaria, or cause more harm (tangling deaths)?
  • Showing "Malaria nets does not reduce malaria" is informative!

Accepting a prescriptive claim requires both a value judgment and accepting a causal claim

Falsifiability

Which claims can science evaluate?

#NotAllEmpiricalClaims open to science

Falsifiability

an empirical claim is falsifiable

if that claim can be shown to be wrong by a specific empirical test. Even if we never do show the claim is wrong, it is falsifiable if, in principle it could be shown to be wrong.

an empirical claim is unfalsifiable

if there is no empirical test that can be done to show the claim is wrong

Falsifiability

Because science considers alternatives/is open to being wrong…

we can only scientifically evaluate claims that can, in principle be shown to be wrong.

The best claims/theories are those that stand up to many tests to show them wrong.

Falsifiability

Contrast with verifiability

If we had an empirical claim, \(H_1\) (\(H\) for hypothesis)

and, if \(H_1\) were true or valid, then it implies we should make certain empirical observations \(O_1\)

Verification says that

  1. \(H_1 \rightarrow O_1\)

  2. If we see \(O_1\)

  3. Therefore, \(H_1\) is valid

Falsifiability

Many people reject verifiability because many different, incompatible claims are compatible with the same observed evidence

  1. \((H_1, H_2, \ldots, H_k) \rightarrow O_1\)

  2. If we observe \(O_1\)

  3. \(H_1\) is not proven

Falsifiability

If a claim \(H_1\) is falsfiable, there might be observable implication \(O_1\) that, if it were untrue would invalidate \(H_1\). So…

  1. \(H_1 \rightarrow O_1\)
  2. \(not\ O_1\)
  3. Therefore, \(not\ H_1\)

Examples

  • "Immigrants are coming across the border to kill you" ~ Donald Trump
  • Flying Spaghetti Monster
  • Humans are rational utility-maximizers