## 10.1 Quick revision

We **strongly** recommend trying these *Quick revision* questions **before** your tutorial.

A study compared the arrivals-on-scene time for two groups of paramedics (Tuttle and Hubble 2018):

- Those with fewer than \(15\) out-of-hospital cardiac arrest (OHCA) resuscitations in the past five years (the
*inexperienced*group, IE), and - Those paramedics with 15 OHCAs or greater (the
*experienced*group, E).

The researchers wanted to see if there was a *difference* in the mean time from scene arrival to starting the first advanced airway procedure for the two groups.
The mean time from scene arrival to starting the first advanced airway procedure was \(10.05\) m for the inexperienced group (IE), and \(10.21\) m for the experienced group (E).

- The
*null*hypothesis is \(H_0\): \(\mu_{IE} = \mu_{E}\). True or false?

- The
*alternative*hypothesis is \(H_0\): \(\mu_{IE} < \mu_{IE}\). True or false?

- Since the two sample means are different, we reject the null hypothesis.
True or false?

**TRUE**. Remember that all hypotheses are about population parameters, and have an "equals to" in there somewhere (the "no difference, no change, no relationship" position).**FALSE**. The hypothesis is about a population parameter (\(\mu\)), which is good.

But the actual question is "to see if there was a**difference**in the mean time..." which suggests a*two*-tailed alternative hypothesis (not a*one*-tailed alternative hypothesis as given).**FALSE**. The*sample*means could be different for one of two reasons: (a) the population means are actually the same, but the*sample means*are just different due to sampling variation; or (b) because the*population*means are different.

We don't know*which*one of these reasons is the reason here.

### References

Tuttle JE, Hubble MW. Paramedic out-of-hospital cardiac arrest case volume is a predictor of return of spontaneous circulation. Western Journal of Emergency Medicine. California Chapter of the American Academy of Emergency Medicine (Cal/AAEM); 2018;19(4):654.