In order to estimate the independent effects, complete the re-constructed table below using the group of “No Co-morbidity”

Part 1 c

c. In order to estimate the independent effects, complete the re-constructed table below using the group of “No Co-morbidity” & “One or more First Trimester Physician Visit” as the reference group for each of the other three groups. (2 points)

Co-morbidity Present

Physician Visit First Trimester

Low BW

Normal BW

 

Incidence

 

(%)

 

RR

 

AR

 

No

 

One or more

 

26

 

63

 

29%

 

1.31

 

0.24

 

No

 

None

 

17

 

59

 

22%

 

1.31

 

0.24

 

Yes

 

One or more

 

45

 

5

 

90%

 

2.14

 

0.53

 

Yes

 

None

 

6

 

8

 

42%

 

2.14

 

0.53

 

 

 

 

 

Incidence of LBW in exposed group 0 physician visits in the 1st trimester: 26/89 =0.29%

 

 

 

Incidence of LBW in exposed group 1 or more physician visits in the 1st trimester: 17/76 =0.22%

 

 RR = 0.29/0.22 =1.31

 

AR = (0.29 -0.22)/(0.29) = 0.24

 

 

 

Incidence of LBW Among 0 physician visit in the 1st trimester: 45/50 =0.9%

 

 

 

Incidence of LBW Among ½ physician visit in the 1st trimester: 6/14 =0.42%

 

 RR = 0.9/0.42 =2.14

 

AR = (0.9 -0.42)/(0.9) = 0.53

 

 

 

 

 

 

 

Problem 2: Using the approach of comparing the expected joint effect and the observed joint effect

 

 

 

Using the approach of comparing the expected joint effect and the observed joint effect of physician visit and presence of co-morbidity:

 

 

 

Recall that 

 

 

 

For additive models:  Expected RRA+Z+  = RRA+Z- + RRA-Z+ – 1.0

 

 

 

Or

 

 

 

Expected ARA+Z+  = ARA+Z- + ARA-Z+

 

 

 

 

 

For multiplicative models:  Expected RRA+Z+ = RRA+Z- x RRA-Z+ 

 

 

 

where A+/- and Z+/- are the independent positive and negative effects of no physician visit and co-morbidity.   Since “no physician visit” and “co-morbidity present” are the risk factors, think of “no physician visit” as A+ and think “co-morbidity present” as Z+. 

 

 

 

Based only on the results from Part 1 c, address the questions below:   

 

 

 

 

 

 

 

 

 

 

 

 

 

a. What is the estimated independent effect (measured by RR and AR) of no Physician Visit (i.e. RRA+Z- and ARA+Z-)? (0.5 points)

 

 

 

 

 

 

 

 

 

 

 

 

b. What is the estimated independent effect (measured by RR and AR) of Co-morbidity (i.e. RRA-Z+ and ARA-Z+)? (0.5 points)

 

 

 

 

 

 

 

 

 

 

c. What are the expected and observed joint additive effects of Co-morbidity and No Physician Visit? (1 point)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

d. What are the expected and observed joint multiplicative effects of Co-morbidity and No Physician Visit? (1 point)

 

 

 

 

 

 

 

 

 

 

e. Compare the expected RR with the observed RR from d. Assuming that no random variability or confounding effects exist, what do you conclude about the presence of multiplicative interaction? (0.5 points)

 

 

 

 

         

 

 

 

 

 

 

f. Using a similar process, compare the expected AR with the observed AR, what do you conclude about the presence additive interaction? (0.5 points)

 

 

         

 

 

 

g. Based on these data, state your conclusions about the importance of a physician visit during the first trimester.  (1 point)

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