1. Batching

2. Contents What is batching? How many batches should I make?
Batching: Pros and Cons
What if I don’t have enough time/resources to survey all my batches?
“Less is More”
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3. What is batching?
Batching is a method of dividing up a heterogenous population into two or more homogenous populations.
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4. Batching Example #1: Employee status (character variable)
Assume you want to survey employees of a government department about the current management style.
Some employees are management, and some are unionized. These two groups may have very different opinions about the management style.
It would be wise to take two separate samples, one from each population.
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5. Batching Example #1 Total population of employees.
Batched into two populations.
Two separate samples
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6. Batching Example #2: Funding levels of contributions (numerical variable)
Assume you want to review the management of contribution agreements awarded by Health Canada for FY
The funding level varies greatly between agreements. Some have relatively low funding levels (e.g., $30-$60K), while some have extremely high funding levels (e.g., $5-$10M).
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7. Batching Example #2
How they are managed, and the risk associated with them, probably differs depending on the funding level of the contribution.
In this case, the contribution agreements should be batched into different populations based on funding level.
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8. Batching Example #2
The first step for batching is to look at the range and frequency of different amounts awarded. This is called a “distribution”.
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9. Three batches could be made from this one population.
108 files
51 files
13 files
Three batches could be made from this one population.
One batch can be all contributions less than $300K.
Another batch can be all contributions from $300K to $1.2M.
The third batch can be from $1.2M to $2.1M
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10. Population Characteristics Sampling Strategy
$0-$300K 108 files-Low risk Take a small sample
$300K-$1.2M 51 files-Moderate risk Take a large sample
$1.2M-$2.1M 13 files-High Risk Perform a census
Sampling strategy from each batch can depend on:
the number of files, and
level of risk associated with the population.
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11. For the population “$0-$300K”,
Population Characteristics Sampling Strategy
$0-$300K 108 files-Low risk Take a small sample
$300K-$1.2M 51 files-Moderate risk Take a large sample
$1.2M-$2.1M 13 files-High Risk Perform a census
For the population “$0-$300K”,
the population is large,
and the risk associated with the files is low,
hence you do not need to invest in a very accurate sample. You may even decide to not sample it at all to conserve resources.
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12. For the population “$300K-$1.2M”,
Population Characteristics Sampling Strategy
$0-$300K 108 files-Low risk Take a small sample
$300K-$1.2M 51 files-Moderate risk Take a large sample
$1.2M-$2.1M 13 files-High Risk Perform a census
For the population “$300K-$1.2M”,
the population is smaller,
and the risk associated with the files is moderate,
hence you should invest in an accurate sample.
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13. For the population “$1.2M-$2.1M”,
Population Characteristics Sampling Strategy
$0-$300K 108 files-Low risk Take a small sample
$300K-$1.2M 51 files-Moderate risk Take a large sample
$1.2M-$2.1M 13 files-High Risk Perform a census
For the population “$1.2M-$2.1M”,
the population is very small,
and the risk associated with the files is very high,
hence you should invest in a very accurate sample. (i.e., do a census).
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14. Contents What is batching? How many batches should I make?
Batching: Pros and Cons
What if I don’t have enough time/resources to survey all my batches?
“Less is More”
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15. How many batches should I make?
That depends on the level of heterogeneity of the population.
The more batches you make, the more homogenous each batch is.
However, with more batches, you have more samples to collect, and a larger total sample size.
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16. Example: Four batches Population (800 members) Four Batches
(200 members each)
Minimum sample size needed:
51 from each batch
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17. Example: Two batches Population (800 people) Two Batches
(400 people each)
Minimum sample size needed:
58 from each batch
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18. Contents What is batching? How many batches should I make?
Batching: Pros and Cons
What if I don’t have enough time/resources to survey all my batches?
“Less is More”
NEXT

19. Batching: Pros and Cons
Two Batches Con
Less homogenous groups.
Able to report estimates for only two groups.
Two Batches Pro
Less members to survey (116).
Less costly.
Four Batches Pro
More homogenous groups.
Able to report estimates for all four groups.
Four Batches Con
More members to survey (204).
More costly.
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20. What if I don’t have enough time/resources to survey all my batches?
Reduce the number of batches as much as possible without sacrificing homogeneity too much.
Prioritize the batches in terms of associated risk. Start by surveying high risk populations.
Take small samples of low risk populations.
Reduce the scope of the audit to exclude low risk populations.
Reduce the level of detail for reporting results (i.e., report national estimates instead of P/T estimates).
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21. Remember: “Less is More”
A smaller amount of reliable, good quality data is more informative than a larger amount of unreliable poor quality data.
Defendable conclusions can be drawn from reliable data.
Unreliable data can be discredited and rejected by the entity.