Seasonal Index Monthly Crime Calculator

Actual12-month count/mean seasonal indices on equal or independently normalized exposure; not multi-year seasonal adjustment or forecast of danger.

Description

Monthly seasonal indices compare recorded counts with their twelve-month mean.

Monthly seasonal indices compare recorded counts with their twelve-month mean.^[1]

They describe the supplied year and do not independently establish a stable recurring seasonal pattern. Use this tool to calculate the stated observation or conditional model from supplied measurements.

When to use Seasonal Index Monthly Crime Calculator

Use this tool to calculate the stated observation or conditional model from supplied measurements. Establish the jurisdiction or research scope, observation and event definitions, reference date, matched period and denominator basis.

How to use Seasonal Index Monthly Crime Calculator and understand its results

Establish the jurisdiction or research scope, observation and event definitions, reference date, matched period and denominator basis.
Enter independentlyMatchedMonthlyCounts, using the field meanings and rules below, then run the tool.
Read result.observedMonthlyIndices. Interpret each field using the units, signs and evidence rules below.
If input validation fails, correct the reported field and run again. Before applying a successful result, check the stated reference scope, units, assumptions and any retained unknown evidence.

Input field	Meaning	Value type	Requirement
independentlyMatchedMonthlyCounts	Independently matched monthly counts	list of number	Required

Require exactly twelve nonnegative finite matched monthly counts and positive arithmetic mean. Divide each count by that mean in caller month order. All-zero input fails; fractional values are accepted and no multi-year seasonal fitting is performed.

monthlyIndex_i=count_i/mean(twelveCounts)

Apply the field units and exact ordering, boundary and evidence rules above.

Output field	Meaning	Value type
result	Structured result containing the calculation or selected reference fields below	object
result.observedMonthlyIndices	Observed Monthly Indices; use the units, sign convention and calculation stated above	list of number

json

{
  "input": {
    "independentlyMatchedMonthlyCounts": [
      10,
      10,
      10,
      10,
      10,
      10,
      10,
      10,
      10,
      10,
      10,
      10
    ]
  },
  "output": {
    "result": {
      "observedMonthlyIndices": [
        1,
        1,
        1,
        1,
        1,
        1,
        1,
        1,
        1,
        1,
        1,
        1
      ]
    }
  }
}

Limitations and assumptions

They describe the supplied year and do not independently establish a stable recurring seasonal pattern. Results depend on the independently established measurement basis and the exact model assumptions above.

Every listed input requires an explicit value. Unexpected fields, incorrect value types, nonfinite numbers and sparse numeric arrays fail validation; tool-specific bounds and alignment rules apply as described above. Extremely large inputs or outputs can also be rejected. An input error is distinct from a successful calculation that reports a false comparison or retains unknown evidence.

Alternative or Complementary methods

Use Crime Trend Percent Change YoY Calculator to examine a related aspect: Year-on-year percent change compares recorded counts on a matched basis.

Use CompStat Period Comparison Tool where its separate inputs and scope apply: CompStat period comparison needs matched categories and reporting periods.

References

Seasonal Index Monthly Crime Calculator — tool.io

Similar or alternative tools

Crime Trend Percent Change YoY Calculator
Year-on-year percent change compares recorded counts on a matched basis.
CompStat Period Comparison Tool
CompStat period comparison needs matched categories and reporting periods.