## 10.1 Quick revision

We recommend trying these Quick revision questions before your tutorial.

A study compared the arrivals-on-scene time for two groups of paramedics :

• 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).

1. The null hypothesis is $$H_0$$: $$\mu_{IE} = \mu_{E}$$. True or false?
2. The alternative hypothesis is $$H_0$$: $$\mu_{IE} < \mu_{IE}$$. True or false?
3. Since the two sample means are different, we reject the null hypothesis. True or false?
4. The article quotes the $$P$$-value as 0.51; this means there is a 51% chance that the null hypothesis is true. True or false?
1. 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).
2. 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).
3. 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.
4. FALSE. This is not what the $$P$$-vaule means (see the textbook).

### 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.