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CASE 13.2 using SPSS (Analyze > Compare Means > Paired Samples T Test)

Objective

To measure the response intervals of fire departments compared with ambulance services in three urban centers to determine whether defibrillators should be added to fire vehicles.

Method

A prospective sample of were collected over a period from March 1, 1994, to August 31, 1994 where all call for ambulance and fire departments were monitored in three urban areas Cambridge, Kitchener and Waterloo.

Since the samples are independent there is no relationship between the observations in one sample and the observations in the other two samples. Therefore a matched pairs experimental design is used to compare the response interval of the fire department with that of the ambulance service for each call.

Results

Compare two populations of interval data. The parameter is the difference between two means m1-m2, where m1 = ambulance mean time
m2 = fire department mean time

To determine whether fire truck arrives at the scene on average more than 1 minute sooner than an ambulance, the alternative hypothesis will specify that m1 is greater than m2: H0: (m1-m2) = 1 or mD = 1

H1: (m1-m2) > 1 or mD > 1

In two of three of the urban centers, the mean is taken for the minutes that the fire departments arrived on scene. And in two urban areas, the fire department arrives on scene more than a minute sooner than the ambulance service:

Cambridge (n = 571, mean = 2.22 min, p < 0.0001)
Kitchener (n = 1,011, mean = 1.24 min, p < 0.003)
Waterloo (n = 300, mean = 0.69 min, p < 0.98)

Conclusions

This we can conclude that the shorter response interval of fire departments suggests training the personnel and placing defibrillators on fire response vehicles in an effort to decrease the time to defibrillation for cardiac arrest victims.
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