Question

1. A randomized clinical trial is conducted to determine if a new medication to strengthen bones in the elderly can prevent, or reduce the number of, low-impact falls (i.e., falls from a standing position or lower). Participants are randomized to receive either the new medication or the standard treatment (vitamin D and calcium supplements). Using the information provided below, determine the incidence rate ratio in the new medication vs. the vitamin D/calcium treated group. Interpret this incidence rate ratio. Hint: use the average length of follow-up and number of participants to determine person-years for each treatment group.

           

	New medication	Calcium/Vitamin D
Number of participants	8,277	9,234
Average length of follow-up for each participant (years)	4.3	4.1
Number of falls	2,002	3,987

Answer 1

For the incidence rate ratio,we need to determine person's time ,which is nothing but the sum of the times of follow up for each participant in that treatment group.

Person's time:

number of participants * average length of follow-up

for new medication = 8277*4.3 = 35591.1

for supplements = 9231*4.1 = 37847.1

incidence rate for new medication = no.of falls / person's time 1

= 2002 / 35591.1 = 0.05625

incidence rate for supplements = no. of falls / person's time 2

= 3987/ 37847.1 = 0.10534

INCIDENCE RATE RATIO = 0.05625 / 0.10534 = 0.53396

since IRR < 1, which implies relative risk is lower by the treatment of new medication when compares with treatment by vitamin supplements.

That is, we can prevent no. of falls more by the treatment of new medication.