View
215
Download
1
Category
Preview:
Citation preview
Analysis of Cohort Data (Kenya PNC)Unintended Pregnancy
Weiwei Zhou, Isolde Birdthistle, Susannah Mayhew - on behalf of the Integra Team
Cohort datasets • Cohort: Kenya PNC (n=869)
• Four rounds: Baseline, 6 months, 16 months, 24 months
• Study group: Intervention, Comparison
• Facility: 6 (Intervention) + 6 (Comparison)
• UID: Facility code + Interviewers’ code + Client No.
• Question: Does integration affect the incidence of unintended pregnancy?
• Method: Time to event (survival) analysis
Outcome: Event (unintended pregnancy)
Event occurred
Y = 1
Since the last time we saw you (x months ago), have you become pregnant?
1. Yes2. No3. Missing
At the time you became pregnant with the last pregnancy, did you:
1. Want to become pregnant then;
2. Want to wait until later;3. Not want to have any/more
children?4. Missing
+ (AND)=
Event did not occurY = 0
Since the last time we saw you (x months ago), have you become pregnant?
1. Yes2. No3. Missing
At the time you became pregnant with the last pregnancy, did you:
1. Want to become pregnant then;
2. Want to wait until later;3. Not want to have any/more
children?
= + (AND)
Outcome: Event (unintended pregnancy)
If Y = missing,Y is considered as 1
What did you do when you discovered that you were pregnant with your last pregnancy?
1. Nothing2. Attempted to stop but not
succeed, 3. Attempted to stop and succeed.
OR=
How did you feel when you discovered you were pregnant with your last pregnancy?
1. Happy2. Unhappy/
disappointed3. Felt nothing4. other
Were you using a family planning method when you became pregnant with this last pregnancy?
1. Yes2. No
AND
Outcome: Event (unintended pregnancy)
Date of unintended pregnancy
How many
months pregnant are you?
=
xx months
Miscarried/aborted
Given birth
OR
OR
R(x-1) interview date
R(x) interview date
xx months
R(x-1) interview date
( b – a )/2
R(x) interview date
ba
R(x-1) interview date
R(x) interview date
9 months
Baseline Round 1 Round 2 Round 3
Time (from baseline interview date to event date)
1) Study Group (Intervention and Comparison)
2) Baseline index (categorical, <1.5, >=1.5)
3) Averaged cumulative index (per day).
Exposure
ACI = total index of visitstotal exposure time
0.0
1.0
2.0
3.0
4.0
5cu
mu
lativ
e in
dex
(per
day
)
0 200 400 600 800time
Exposure: cumulative index
Blue circle: Event (size of circle=level of integration) Red/Green dot: Higher/Lower ACI exposure group
Analysis plan
• Cox proportional hazards model• Univariate analysis• Multivariable analysis, Adjusted for:
Demographic: age, education, religion, employment statutes, household incomeSESFertility preference: number of children, desired additional number of children, want/when to have
another child, also husband’s wish.Other: HIV status, any children died, numbers of
pregnancies
• Test of model assumption
Univariate and multivariable analysis, PNC Kenya
Univariate Adjusted
n HR P-value HR P-value
Design study group
Comparison 306 Ref Ref
Intervention 563 0.63 (0.38, 1.06) 0.083 0.62 (0.32, 1.20) 0.153
Baseline index
<1.5 368 Ref Ref
>=1.5 501 2.03 (0.83, 5.00) 0.121 1.45 (0.51, 4.15) 0.488
Cumulative index
Lower 432 Ref Ref
Higher 432 1.11 (0.69, 1.78) 0.667 0.84 (0.46, 1.50) 0.549
Kaplan-Meier plot, PNC Kenya
0.85
0.90
0.95
1.00
0 200 400 600 800analysis time
Control Intervention
Kaplan-Meier survival estimates, design group
Kaplan-Meier plot, PNC Kenya
0.85
0.90
0.95
1.00
0 200 400 600 800analysis time
baseline index <= 1.5 baseline index > 1.5
Kaplan-Meier survival estimates, baseline index
Kaplan-Meier plot, PNC Kenya
0.85
0.90
0.95
1.00
0 200 400 600 800analysis time
Lower cumulative index Higher cumulative index
Kaplan-Meier survival estimates, cumulative index
Limitations and Conclusions
• Index of visits to non-study clinics are not available. Mean index values of study clinics have been used.
• Event doesn't have an uniform distribution, thus the averaged cumulative index may not represent daily/monthly exposure to clinics.
• Interaction terms• Kenya PNC: No significant effect by using
study group, baseline index, or cumulative index as exposure variable.
Recommended