Immortal time and healthy-adherer bias in a composite cardiac rehab cohort, and the line between what that design supports and what only a trial could, set out for NU505 Unit 3. Searches like "nu 505 unit 3 assignment example", "nu505 unit 3 sample" and "nu505 unit 3 example" land here.
What a finished NU505 Unit 3 study design critique looks like
The critique runs four to five pages around a claims table. The study is summarized first: 6,200 adults discharged after a first myocardial infarction, 2,480 of whom attended at least one rehab session within six months; three-year mortality of 6.9 percent among attenders and 11.2 among non-attenders, a risk ratio of 0.62. The claims table lists each conclusion from the abstract in one column and, beside it, whether the cohort design can support it. A section on immortal time follows, explaining that attenders had to survive a median of 38 days to reach their first session, while deaths in that window counted against non-attenders. A second section covers who attends: younger, insured patients with fewer comorbidities. A landmark reanalysis at six months, reported in the authors' own appendix, shrinks the ratio to 0.81.
How a NU505 Unit 3 example is structured
Claims organize the critique rather than design features, because the prompt asks which claims survive. Each claim is tested against what a cohort can establish: temporal order, an association adjusted for measured factors, and a dose pattern, but not the size of a causal effect when attendance itself depends on health. Immortal time comes first among the threats because it is structural and fixable, and the landmark figure in the appendix shows how much of the association it produced. Healthy-adherer bias follows and is harder to fix, since willingness to attend likely tracks unmeasured traits that also predict survival. The critique credits the cohort for what it does well, including documenting who is not referred, which is itself useful. The close separates the clinical decision from the study: referral after myocardial infarction is already recommended by cardiology guidelines, so the question is what number to quote to patients.
Claims in one column, verdicts in the next
Five conclusions from the abstract are listed, each given a verdict: the design carries it, carries part of it, or cannot carry it. The table lets a reader see the critique's judgment before reading its reasons.
Thirty-eight days nobody could die in
Attenders had to be alive at their first session, a median of 38 days after discharge. Deaths in that interval landed only in the non-attender group, which flatters rehab before any exercise begins.
A landmark that halves the effect
Classifying patients by attendance at six months and counting deaths only afterward moves the ratio from 0.62 to 0.81. The critique reports both and explains why the second is closer to honest.
Who shows up to rehab
Attenders were younger, more often insured and less often diabetic. Adjustment handles what was measured; motivation, transport and social support were not, and each could predict survival independently.
The number to say to a patient
Referral stands on existing guideline recommendations. What changes is counseling: the critique argues that 38 percent should not be quoted as the benefit a patient can expect.
Where marks go in NU505 Unit 3
Three rows commonly appear on NU505 critique rubrics: the design and its strengths, the specific threats, and the fit between claims and evidence. The first row is straightforward here, and the example spends little space on it. On threats, a generic nod to confounding earns partial credit, while explaining immortal time with the 38-day window and the landmark figure earns full credit, because it shows the mechanism and its size. Matching claims to evidence is the distinctive demand of this unit, and a table that sorts each claim makes that visible to a grader. A frequent overreach is concluding that rehab does not work, which overstates the critique; another is repeating the abstract's causal language in the paper's own summary. Recommendations for a new trial need to say what it would randomize and measure.
Get a NU505 Unit 3 example written to your instructions
Share the article your Unit 3 prompt assigns, or its citation, plus the questions and the grading rubric your section uses. The critique is organized around that study's own claims, sorting what its design can carry from what it cannot. A first custom sample is provided at no cost and is ready within 24-48h.
NU505 Unit 3 questions, answered
What is immortal time bias in plain terms?
It arises when one group, by definition, must survive a period to be classified as exposed. Patients counted as rehab attenders had to live until their first session, so any deaths before then could only fall in the comparison group. That makes the exposure look protective even if it did nothing. Landmark analysis or time-varying exposure definitions are standard ways to correct it.
Does the critique conclude that cardiac rehab is ineffective?
No, and that distinction matters for the grade. The critique argues that this cohort overstates the size of the benefit, not that the benefit is zero. Referral after a heart attack is recommended by major cardiology guidelines on the strength of broader evidence. The example keeps the clinical recommendation intact while questioning the specific number the authors promoted.
Which claims can a cohort study legitimately support?
Cohorts are strong on temporal order, on describing who receives an exposure, and on associations adjusted for measured factors. They can suggest a dose pattern. They cannot fully separate the exposure from reasons people chose it when those reasons also affect the outcome. Sizing a causal effect under those conditions usually requires randomization, or careful emulation of a trial with explicit assumptions.