One case-control table on backyard poultry and Salmonella anchors this HS340 Unit 4 example, which builds the four cells, computes an odds ratio of 6.1 and states what it means. Searches like "hs 340 unit 4 assignment example", "hs340 unit 4 sample" and "hs340 unit 4 example" land here.
What a finished HS340 Unit 4 two by two table looks like
A single page holds the table and a second page reads it. The layout puts poultry contact in the rows and case status in the columns, with the cells lettered: 19 exposed cases, 29 unexposed cases, 14 exposed controls and 130 unexposed controls. Column totals of 48 and 144 appear beneath, and a note explains why the row totals carry no meaning here: the investigators chose three controls for every case, so the share of cases in any row is an artifact of that choice. The cross-product follows, 19 times 130 over 29 times 14, giving 6.1. A 95 percent confidence interval of 2.7 to 13.5 is computed on the log scale. Two sentences of interpretation close the page, one on the odds and one on the likely direction of risk.
How a HS340 Unit 4 example is structured
Construction comes before calculation, and the example keeps them visibly apart. Layout is fixed first, since every formula on the page depends on which cell is a, and flipping the exposed and unexposed rows returns the reciprocal without any warning. Margins come next, and the column totals are the only ones a reader may interpret, because the investigators fixed them. That point leads straight to the choice of measure: with case numbers set by design, the proportion of bird handlers who fell ill cannot be estimated, so the odds ratio is the figure this table can honestly give. Calculation follows in one line. The interpretation paragraph then does two jobs. It states the result as odds of exposure, cases against controls, and it explains that for an uncommon infection the odds ratio approximates how much the exposure multiplies risk.
Cells lettered before any arithmetic
Rows hold poultry contact, yes or no; columns hold cases and controls. Letters a through d are written into the corners so the cross-product can be traced by eye.
Why the row totals are silent
Thirty-three people handled birds, but the share of them who are cases, 19 of 33, reflects the three-to-one sampling rather than any attack rate. The example says so and leaves that fraction uncalculated.
The cross-product in one line
Nineteen times 130 is 2,470; 29 times 14 is 406. The quotient, 6.08, is reported as 6.1, with the exposure odds for each group shown beside it: 0.66 for cases and 0.11 for controls.
An interval that stays wide
The log-scale interval runs from 2.7 to 13.5. Its whole range lies above 1.0, the example notes, and most of its width comes from only 14 exposed controls.
Reading the ratio in plain words
Cases had about six times the odds of recent poultry contact that controls had. Because Salmonella infection is uncommon in the population, the example adds that risk among people handling birds is probably raised by a similar factor.
Where marks go in HS340 Unit 4
Table exercises are often marked for construction, calculation and interpretation, and construction is where HS340 graders catch the most errors. Placing the unexposed row on top while applying formulas written for the standard layout produces 0.16 instead of 6.1, and the example avoids it by labeling every margin in words before filling a cell. Calculation credit needs the cross-product shown, not just the answer. Interpretation carries the rest. Common deductions include a relative risk computed across the rows of a case-control table, an odds ratio of 6.1 described as six times the chance of illness with no mention of the rare-outcome assumption, and a conclusion that backyard birds cause Salmonella infection drawn from one study alone. A wide interval passed over in silence also costs points in many sections.
Get a HS340 Unit 4 example written to your instructions
Forward the counts or line list behind the HS340 Unit 4 table, with the questions exactly as posted and the rubric. The desk letters the cells, chooses the measure the sampling permits and reads it in plain words. That first custom sample is free and reaches the inbox in 24-48 hours, the interval computed and its width explained.
HS340 Unit 4 questions, answered
Why not calculate a relative risk from the Salmonella table?
Because the investigators decided how many controls to enroll. With three controls per case, the share of exposed people who are cases reflects that decision rather than how often exposed people fell ill. The odds ratio does not depend on the sampling fraction, which is why case-control tables report it. For an uncommon infection, it also approximates the relative risk a cohort would have found.
Does the order of rows and columns matter?
Only if the formulas do not follow it. The standard cross-product assumes exposed people in the top row and cases in the left column. Swapping one of those, so the unexposed row sits on top, turns 6.1 into 0.16 without any warning. Labeling each margin in words and lettering the cells makes the slip much harder to commit, and a grader can check the layout at a glance.
How should a confidence interval this wide be described?
As an honest range, with its cause named. An interval from 2.7 to 13.5 says the data are consistent with a modest association and with a very strong one, and the width comes mostly from small cell counts. It still excludes 1.0, so chance alone is an unlikely explanation. A larger study, or pooled data from several states, would narrow it considerably.