An openlabel study where participants are aware of the treat

An open-label study (where participants are aware of the treatment they are taking) is run to assess the time to pain relief following treatment in patients with arthritis. The following linear regression equations are estimated relating time to pain relief measured in minutes (dependant variable) to participant’s age (in years), gender (coded 1 for males and 0 for females), and severity of disease (a score ranging from 0-100, with higher scores indicative of more severe arthritis):

Time to Pain Relief = -24.2 + 0.9 Age

Time to Pain Relief = 11.8 + 19.3 (Male gender)

Time to Pain Relief = 3.2 + 0.4 Severity

Time to Pain Relief = -19.8 + 0.50 Age + 10.9 (Male Gender) + 0.2 Severity

A) What is the expected time to pain relief for a male following treatment?

B) What is the expected time to pain relief for a participant aged 50 following treatment?

C) In assessing the association between gender and time to pain relief, is their evidence of confounding by age or severity? Briefly justify your answer.

Solution

a)

expected time to pain relief for male following treatment

= 11.8 + 19.3 = 31.1 minutes

b)

expected time to pain relief for a participant aged 50 = -24.2 + 0.9 * 50 = 20.8 minutes

c)

The unadjusted association between gender and time to pain relief is 19.3 minutes.

After adjustment for age and severity, the association is 10.9, a change of 43% in the parameter estimate.

Because the change in the regression coefficient exceeds 10%, this is evidence of confounding by age and severity