The Morbidity Method: A Step-by-Step Guide
Use when: medicines are disease-specific, a treatment or guideline is new, or consumption data are unreliable.
Setting up the assumptions
- Population: served population, split by age or weight where dosing differs.
- Episodes: incidence (acute) or prevalence (chronic) rates, or register counts.
- Care-seeking: share of cases treated at the facilities supplied.
- Regimen: standard treatment guideline for each patient group.
- Allowance: retreatment, losses or non-standard prescribing (%).
- Planning parameters: lead time, procurement period and safety stock.
Procedure
- Episodes = population × incidence × care-seeking rate, per patient group.
- Quantity per episode = dose × frequency × duration.
- Need = episodes × quantity per episode, summed across conditions.
- Add the allowance to obtain annual need.
- Quantity to procure = monthly need × (lead time + procurement period) + safety stock − stock on hand − stock on order.
- Compare with recent consumption, where available.
Worked example
A district of 200,000 people is quantifying an oral antibiotic for uncomplicated urinary tract infections in adult women; the guideline course is two capsules daily for five days.
Assumptions: adult women 34% of the population; 40 episodes per 1,000 per year; 75% treated at public facilities; 10% allowance; lead time 3 months; procurement period 12 months; safety stock 3 months; stock on hand 4,000; packs of 100.
| Step | Calculation | Result |
|---|---|---|
| Target population | 200,000 × 34% | 68,000 women |
| Expected episodes | 68,000 × 40 ÷ 1,000 | 2,720 episodes |
| Treated at public facilities | 2,720 × 75% | 2,040 episodes |
| Quantity per episode | 2 capsules × 5 days | 10 capsules |
| Annual need with allowance | 2,040 × 10 × 1.10 | 22,440 capsules |
| Monthly need | 22,440 ÷ 12 | 1,870 capsules |
| Requirement | 1,870 × (3 + 12) | 28,050 capsules |
| Safety stock | 1,870 × 3 | 5,610 capsules |
| Quantity to procure | 28,050 + 5,610 − 4,000 | 29,660 capsules |
| Rounded to packs | 29,660 ÷ 100, rounded up | 297 packs |
Key considerations
- Tends to overestimate: assumes every case is treated by the guideline.
- Needs reliable, local disease data.
- Split episodes by age, weight or severity.
- Sum across all conditions using the same medicine.
- Update immediately when guidelines change.
Based on the online course on forecasting and quantifying medicines and health products offered by i+academy; all credit belongs to the course and its facilitators. For a fuller understanding, enrol in the course on i+academy.
Other guides in this series: Consumption method · Demographic method · Other methods