Question

A cow-calf veterinarian suspects there is an association between pasture exposure of cows to wastewater from hydraulic fracturing (“fracking”) and reproductive failures (failure to conceive, abortion, etc.). She is planning a study to assess such a possibility.

The initial results did not find a statistically significant association for fracking wastewater and reproductive outcomes. However, findings became statistically significant when results were separated according to feed source. Cattle fed exclusively homegrown forage and exposed to fracking wastewater had more reproductive failures than those herds exposed to wastewater but who bought hay from other sources. There was no difference in reproductive performance attributable to homegrown vs. purchased forage in herds with no wastewater exposure.

1. (4 pts.) Which of the following offers P-values consistent with the refined statement of findings?

1. “Fracking wastewater exposure is associated with increased risk where forage was homegrown (P=0.02). There was no association of exposure observed in herds with purchased hay (P=0.20).”
2. “Fracking wastewater exposure is associated with increased risk where forage was homegrown (P=0.20). There was no association of exposure observed in herds with purchased hay (P=0.02).”
3. “Fracking wastewater exposure is associated with increased risk where forage was homegrown (P=0.02). There was no association of exposure observed in herds with purchased hay (P=0.02).”
4. “Fracking wastewater exposure is associated with increased risk where forage was homegrown (P=0.20). There was no association of exposure observed in herds with purchased hay (P=0.20).”

Answer 1

Assuming that the default significance level, α=0.05. We reject the null hypothesis in favour of alternative hypothesis, when p-value is less than or equal to α.

Given, The initial results did not find a statistically significant association for fracking wastewater and reproductive outcomes. Cattle fed exclusively homegrown forage and exposed to fracking wastewater had more reproductive failures than those herds exposed to wastewater but who bought hay from other sources. There was no difference in reproductive performance attributable to homegrown vs. purchased forage in herds with no wastewater exposure

For these findings,

“Fracking wastewater exposure is associated with increased risk where forage was homegrown (P=0.02). There was no association of exposure observed in herds with purchased hay (P=0.20).”

Option (a) is the answer