Sequencing says one slice grew from 10 to 20 percent. Why stay cautious?

• Percentages always sum to a whole, so other slices may have shrunk
• Sequencers cannot detect that species
• Percentages above 10 are unreliable

What does a microbiome name?

• One disease-causing species
• The whole community at one site
• The nutrients microbes consume

Resident microbes defend their niche by occupying sites and nutrients, leaving invaders little room.

Circle one:   True   False

Which design separates a microbiome cause from a consequence?

• Randomized transfer of defined microbes with a comparison group
• Sequencing the same patients deeper
• A larger snapshot survey

Sick people carry a different gut mix than healthy people. What may you conclude so far?

• The sickness causes the mix
• The mix causes the sickness
• Only that sickness and mix travel together so far

A transplant trial fixed no endpoint in advance and reports the one marker that moved. What is the flaw?

• The strain was not named
• Cherry-picking an endpoint after the fact weakens the claim
• Transplants need no comparison group

A probiotic claim is convincing once it shows a shifted profile after treatment, with no strain or control details.

Circle one:   True   False

Patients improve equally whether or not the strain engrafted. What do you conclude?

• Engraftment proof is unnecessary
• The microbes caused the improvement
• The microbes were likely passengers; something else helped