Practice Blinding in Statistics

Use these practice problems to test your method after reviewing the concept explanation and worked examples.

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Quick Recap

Blinding means keeping participants, researchers, or both from knowing which treatment a subject received. It reduces bias caused by expectations or differential treatment.

If people know who got which treatment, they may behave differently, report differently, or evaluate differently. Blinding reduces that extra noise and bias.

Showing a random 20 of 50 problems.

Example 1

medium
In a surgery-vs-medication trial, true blinding is hard. Explain one reason and one partial remedy researchers use.

Example 2

easy
Name the bias most directly reduced when subjects do not know whether they received the drug or placebo.

Example 3

medium
Why can a study be randomized and placebo-controlled yet still produce biased results if it is not blinded?

Example 4

challenge
Design the blinding scheme for a trial of a bitter herbal tea against a control, where taste is hard to mask. Specify how you would blind patients and assessors and what 'placebo' you would use.

Example 5

easy
Which design best controls both patient expectation and researcher bias: single-blind or double-blind?

Example 6

medium
Blinding cannot fix lack of randomization. Briefly justify.

Example 7

medium
A study claims to be double-blind, but the drug causes a distinctive taste the placebo lacks, so patients figure out their group. Why is the blinding compromised, and what is the consequence?

Example 8

challenge
A reviewer notes that a trial reports double-blinding but has a 95% correct-guess rate due to a very distinctive drug. Propose two design changes that would improve credibility in a redo.

Example 9

easy
An observational study with no intervention asks: 'Can it be blinded?' Answer briefly.

Example 10

challenge
Two trials of the same drug: Trial 1 is double-blind and finds no effect; Trial 2 is unblinded and finds a large effect. Explain the most likely reason for the discrepancy and which result to trust.

Example 11

medium
A pediatric vaccine trial cannot use placebo for ethical reasons. Suggest one way to retain a partial blind.

Example 12

easy
A study blinds patients but not the researchers. What is this design called?

Example 13

medium
Match each bias to the design feature that addresses it: (i) confounding, (ii) expectation bias, (iii) selection bias.

Example 14

easy
When neither the patients nor the researchers know who received the treatment, the study is called what?

Example 15

medium
Distinguish what randomization, a control group, and blinding each protect against in one experiment.

Example 16

medium
In a trial of surgery vs. medication, name the closest analogue to double-blinding.

Example 17

hard
A trial reports blinding-integrity test: 70% of treatment patients correctly guessed their arm. Comment on the threat.

Example 18

easy
Why might an unblinded patient who knows they got the real drug report more improvement than they truly feel?

Example 19

hard
A surgeon must know which patients had the experimental implant to perform the surgery. How can the trial still produce credible blinded comparisons?

Example 20

challenge
Critically evaluate the claim: 'Because we randomized, blinding is unnecessary.' Give one scenario where this fails.
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