1. Calculator for the number of survey respondents required
This calculator allows you to estimate the approximate number of survey respondents that would be required to carry out an SSS survey to measure maternal mortality using the direct sisterhood technique. Enter the information requested then click Calculate to obtain the estimated sample size. The entries can be changed and the Calculate button clicked again any number of times.Notes:
- MMR means maternal mortality ratio. A rough estimate of the expected figure must be provided to calculate the required sample size.
- Relative precision refers to the width of the 95% confidence interval. If MMR is around 500, a relative precision of 25% means that you could expect to estimate the MMR to be within approximately ± 125 of the true value.
- General fertility rate (the average number of births per woman of reproductive age per year) can be taken from the most recent DHS survey, a recent census or other major survey.
- Each respondent reports on her sisters (born to the same mother, but not including herself). The average number of sisters a woman has who reached the age of 15 years or more (whether they are alive or dead now) must be estimated. This does not need to be a whole number (e.g. it could be 2.3).
- The questionnaire asks about deaths over a number of years preceding the survey. The shorter the period chosen the more current the estimate will be but the greater the sample size needed. For periods greater than 5 years consider also how reliable women's recall of information will be.
- The exposure adjustment factor is used to correct for the fact that not all of the sisters would have been aged 15-49 throughout the reference period either because they were younger, older or not alive during part of the period. In our surveys we found that sisters had an average of 0.9 × 5 years (i.e. 4.5 years) at risk over the last 5 years. In the absence of any other information this adjustment factor can be left at the default setting (0.9) to estimate sample size.
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2. Calculator for planning how the required number of survey respondents can be obtained from the chosen type of service sites
This calculator allows you to plan a sampling strategy. Greatest efficiency will be achieved by including the largest service sites first (e.g. district hospitals) then making up the required number of respondents by adding smaller sites (e.g. rural health centres) until the required sample size is obtained.
For each site or type of site enter the information requested in the first 3 columns. The number of respondents it is expected to obtain from each facility or type of facility and total number of respondents expected are calculated when the Calculate button is clicked. More facilities can be added or any of the figures already entered can be changed and the Calculate button clicked again until the required number (see sample size calculator above) has been obtained.
No allowance is made in the calculator for repeat visits. If the survey is carried out at any location for more than a few weeks it is to be expected that some of the people attending will already have been interviewed. They should not be interviewed again and allowance should be made for this when estimating numbers of respondents expected.
Notes:
- For each facility or type of facility estimate or obtain from records the number of potential respondents (number of visits) per year (e.g. women aged 15-49 attending antenatal, postnatal, child health or family planning clinics).
- Enter the number of similar sized service sites. If you wish to include similar service sites but for different durations of sampling enter these on separate rows in the table.
- Enter a proposed number of weeks to survey in each site (this can be changed again later). Our surveys were carried out for 3 or 4 weeks at each site. Note, sites may or may not be run concurrently so this is not necessarily the same as the duration of the whole survey.