What is Science?

Plan for Today

1) Recap

2) Attributes of scientific evidence

3) Example


Science as Vocation: Four Insights

(1) Science (in principle) only assume objective knowledge exists and can be known: all other "truths" open to investigation/challenge.

(2) Science is not value-free: assumes certain questions worth answering.

(3) Science is fundamentally interested in prediction

(4) 'Science is meaningless because it gives no answer to our question, the only question important for us: "What shall we do and how shall we live?"' - Tolstoi

Scientific Evidence

Two Key definitions


(For our purposes) a statement about what is true or valid. *If you can add "is true" to the end or "it is true that" to the beginning of the statement without changing the meaning, it is a claim.

Don't overthink this definition. It is as simple as it seems.

Two Key definitions


(For our purposes) the basis for a claim is the reason we should accept the truth or validity of that claim. It is the evidence that is used to "prove" the claim is true and the assumptions required for the evidence to be valid "proof" (sometimes called the "warrant")

An example:

claim: "It rained last night"

basis: "The street is wet"

What is the evidence? What is the assumption behind that evidence? Is it a reasonable assumption?

Using Science to Evaluate Claims

Science is distinct in

(1) Only certain claims can be investigated (insights 1,3,4; next week!)

(2) Having special rules for using evidence and making assumptions to accept claims


Which of these is a fundamental quality of scientific inquiry?

Explain why.

  1. Exact measurement
  2. Making conclusions with high certainty
  3. Employing transparent procedures
  4. Controlled experiments

Scientific bases for claims:

Scientific Bases for Claims:

Transparent procedures

Systematic use of evidence

Test claim against alternatives

Acknowledge uncertainty

Transparent procedures

How did you arrive at your conclusion

  • What data / observations did you use?
  • What comparisons did you make?
  • What choices as a researcher did you make, and why


  • Others can know the assumptions required to find result
  • Others can question your choices
  • Others can replicate your work

Consider alternatives


  • Openness to being wrong
  • One positive piece of evidence can be consistent with many claims

Test your claim against other competing claims

  • Whichever claim "survives" many different tests is best

Systematic Use of Evidence

Observations we make:

  • Based on clear rules for selection
  • clear rules for comparison
  • avoids "cherry-picking"


  • Cherry picking assumes a truth
  • Prevents us from considering alternatives
  • Need to be able to consider challenge to our evidence

Acknowledge uncertainty

Two ways:

Limitations of your finding:

  • Openness about how your evidence could still be wrong
  • What questions remain unanswered after your study (what didn't it tell us)
  • What assumptions did we make that might not be true?

How certain or precise are our answers?

  • Acknowledge possibility of chance relationships
  • Given this, how "confident" can we be about our results being real?


Consider a claim:

A person's prejudice against a group of people can be reduced through real, interpersonal contact with a member of that group.

  • So-called "contact hypothesis" applied to many excluded minorities

  • Contact may humanize the other group, encourage taking their perspective, dispel prejudices

An investigation

LaCour and Green (2014) conduct an experiment:

Can a single conversation change minds on divisive social issues, such as same-sex marriage?

Are conversations about same-sex marriage more persuasive when they are with a gay person?

An investigation: set up

  • Gay-rights organization canvassed for same-sex marriage in California
  • Researchers worked with them to randomize which people received different "treatments"


  • 972 registered voters
  • living in precincts that voted to ban same-sex marriage in 2008

An investigation: set up


Subjects either saw:

  • Canvasser for same-sex marriage who was straight or gay
  • Canvasser for recycling program who was straight or gay
  • No canvasser


  • Answered survey questions about homosexuality, same-sex marriage
  • From 5 days after canvass to 280 days

Transparent Procedures:

Paper: 4 pages

Supplementary Appendix: 24 pages


Who was treated?

How did they get treated?

What were the survey questions?