Studying a Cause You Cannot Assign
Experimental Design domain · Lesson 4 of 20 · Biomedical Innovations (BI)
Today's goal: Students will explain how a case-control study works backward from outcome to exposure, compute and interpret a simple odds ratio with its 95 percent confidence interval, and name recall bias as its signature flaw.
This is a model of the work you should turn in. Use it to check your own: match the structure and the level of detail, do not copy it. Your wording should be your own.
Team-task dataset (a different suspected exposure):
2-by-2 table:
- Cases (cleft): 30 exposed, 70 not exposed.
- Controls (no cleft): 15 exposed, 85 not exposed.
Odds ratio: case odds = 30/70 = 0.4286; control odds = 15/85 = 0.1765; OR = 0.4286 / 0.1765 = about 2.4.
Significance call: the reported 95 percent CI is 0.9 to 3.4. Because that interval includes 1.0, the association is NOT statistically significant; no effect is still plausible.
Recall-bias concern: mothers of affected babies may over-report the exposure while searching for a reason their baby has a cleft, which could inflate the odds ratio, so an OR above 1 is a clue, not a verdict.
This model shows the level of evidence and organization needed to complete: A 2-by-2 table with a computed odds ratio and a significance call from the confidence interval.
- Name the variables and include units.
- Enter observations without changing the raw values.
- Check labels, calculations, and patterns before interpreting the data.
Keep the structure. Replace the question, facts, measurements, and evidence. Then recheck units, vocabulary, and whether the conclusion goes beyond the evidence.
Also due today: Set the division up as case-odds over control-odds, not a straight percentage subtraction.
The finished product above did not appear all at once. Here is the path from the question to the turned-in work, so you can follow the same steps.
- 1Start from today's question: Which group is selected because the event happened?
- 2Work the Model and the Explore questions to reason it out before writing anything.
- 3Pull the specific evidence the product needs from the reading and any database you used.
- 4Write it up in the required format: For a different exposure (cases: 30 exposed, 70 not; controls: 15 exposed, 85 not) build the 2-by-2 table, compute the , decide using a reported 95 percent CI of 0.9 to 3.4 whether the association is significant, and write one recall-bias concern to raise before anyone calls the exposure a cause.
- 5Check it against the rubric, then submit.
| Criterion | Proficient | Developing | Beginning |
|---|---|---|---|
| Complete | Every required part of the artifact is present and filled in. | Most parts are present, but one is missing or left blank. | Several parts are missing. |
| Accurate | The science and data are correct and match the evidence. | Mostly correct, with a small factual slip. | Key science or data is wrong. |
| Scientific reasoning (CER) | States a claim, backs it with specific evidence, and explains the reasoning. | Has a claim and evidence, but the reasoning is thin or missing. | Gives an answer with no evidence or reasoning. |
| Professional communication | Clear, organized, and labeled the way a clinician or scientist would write it. | Readable but disorganized or missing labels. | Hard to follow. |
| Submitted | Turned in through the route named under Submit here and confirmed. | Turned in, but in the wrong place or unconfirmed. | Not turned in. |
- CompleteProficient: Nothing is left blank: the model fills every part of "For a different exposure (cases: 30 exposed, 70 not; controls: 15 exposed, 85 not) build the 2-by-2 table, compute the odds ratio, decide using a reported 95 percent CI of 0.9 to 3.4 whether the association is significant, and write one recall-bias concern to raise before anyone calls the exposure a cause.".
- AccurateProficient: Every number and claim matches the case evidence.
- Scientific reasoning (CER)Proficient: It names a claim, cites the specific evidence, and explains the reasoning, not just the answer.
- Professional communicationProficient: It is organized and labeled like a real chart note.
- SubmittedProficient: It would be attached to your class form or handed in, and confirmed.
One exam-style question that uses exactly what you practiced today. Try it before you reveal the answer, then read why each choice is right or wrong.
Tap an answer to see the full explanation. Nothing is recorded or graded.
It builds this reusable test skill: Interpreting an odds ratio and its confidence interval in a case-control study.
- Name the concept or data pattern being tested.
- Cross out choices that violate that rule or the evidence.
- Justify the best remaining choice before checking the answer.