Contraceptive Continuation rates

The cumulative probability that acceptors of a contraceptive method will still be using any contraceptive method offered by the program after a specified period of time (e.g., one year)

This is also known as the "all-method" continuation rate.

When using cross-sectional population data, evaluators calculate the continuation rate for each unit-interval of use (e.g., first, second, third month of use, and so forth) as the complement of the ratio of acceptors who discontinue use of a program method of contraception at that duration to the number of women still using at the beginning of the month (i.e., 1 minus the discontinuation rate). Evaluators then cumulate these continuation rates to obtain the probability that acceptors of a contraceptive method will still be using any program method after the specified period of time.

The indicator (CRx) is calculated as:

CRx = x(1-qx)/π

Where:
x   = 1
qx = Tx/Nx = conditional probability of discontinuing use during a given interval (e.g., one month, one quarter);
Tx = the number of women discontinuing use during the interval; and
Nx = number of women using at the beginning of the interval.

Note: π signifies that (1- qx ) is multiplied over all intervals from 1 to x.

Illustrative Computation
Continuation rates for reversible methods for durations from 1-12 months, Bangladesh, 1992-97

X
Tx Nx
qx CR
1

291.3 

4422.5 .0659 93.4
 2

160.1 

4025.9 .0398 89.7
 3

205.9 

3803.1 .0541 84.8
 4

89.9

3502.6 .0257 82.7
 5

61.2

3322.9 .0184   81.1
 6

107.5

3173.7 .0339 78.4
 7

68.7  

2998.3 .0229 76.6
 8

57.2

2868.5 .0199 75.1
 9

74.6 

2757.4 .0271 73.0
 10

59.8 

2579.8 .0232 71.3
 11

55.8

2458.0 .0227 69.7
 12

109.5

2350.8 .0466 66.5

Source of data: Bangladesh Demographic and Health Survey, 1996/97


Information on contraceptive initiation, duration of use (including method switching), and discontinuation during a given reference period (e.g., the 3-5 years prior to a survey). Based on this information, one can calculate the percentage who have continuously used for a specific duration (e.g., 12 months, 18 months), as well as the median duration of use.


Population-based: surveys with retrospective contraceptive use histories or calendars

Program-based: client records accompanied by a follow- up study of program dropouts. This source is rarely used.


Contraceptive continuation rates provide a useful summary measure of the overall effectiveness of program services in enabling clients to sustain contraceptive use even though they may switch from one method to another. However, the calculation of continuation rates from surveys requires knowledge of life table (survival) analysis by those subregions of the country (much less individual facilities), making this indicator more useful at the national than regional or local level.

Although evaluators can calculate continuation rates from either facility-based or population-based data, facility-based data have a number of limitations; thus, researchers tend to use large-scale surveys to provide more valid measurements of continuation among the intended population (e.g., Blanc, Curtis, and Croft, 1999).


Obtaining continuation rates at the program level is theoretically possible if evaluators use follow-up studies of new acceptors at a specified period of time after adoption of the method (e.g., 12 months). However, this technique is rarely used (except in clinical trials), given the difficulty and expense of locating these acceptors a year later.

The preferred source of data is the "calendar," a data collection format used in cross-sectional surveys such as the DHS. However, such surveys have limitations of their own. They (a) depend upon the accuracy of respondent recall, (b) do not allow linking of respondents to specific service delivery points, and (c) may not capture the full contraceptive history (e.g., when five-year calendar is used).

It is important to note the distinction between discontinuation and failure of a contraceptive method. Discontinuation of contraception may occur because the individual chooses to stop using a selected method or because accidental pregnancy intervenes. As such, method failure is a subset of discontinuation. Method failure necessarily results in discontinuation. However, not all discontinuation is attributable to method failure.


long-acting/permanent methods (LAPM), family planning