Cardiff University

Data Lab for Social Good

ukri

wgsss

usaid






WHAT WAS LOST

Tracing unmet demand in contraceptive supply chains


Harsha Halgamuwe Hewage
Data Lab for Social Good Research Group, Cardiff University, UK

Lead Supervisor: Prof. Bahman Rostami-Tabar
Co Supervisors: Prof. Aris Syntetos & Dr. Federico Liberatore


2025-05-23

Outline


  • What was never counted...

  • The fundamental question

  • What we are going to do

  • Numerical experiment

  • What’s NEXT

What was never counted…



Seen the UNSEEN

Human story: What data misses


Nilu went to a pharmacy for Product A. It was not in stock and the system logs it as zero demand.


When data is censored by stockouts or service interruptions… Forecasts fail… Not just by being wrong, but by being blind.


This creates broken trust and leads to UNMET DEMAND.

Analytical reality: Why this matters


Stockouts censor demand.
Observed sales ≠ actual demand.


Inventory decisions based on this false signal?
Understocking → more stockouts.


Forecasts don’t just underperform. They miss the whole story.


Contraceptives aren’t easily substitutable. A lost sale = a lost opportunity for care.

Contraceptive products aren’t easily SUBSTITUTED


Story panel

The BIG PICTURE


Story panel

In reality…

There are more than

218 million women

like Nilu still have an unmet need for family planning.

Ultimately, this results in dropouts, unwanted pregnancies, and almost 7 million hospitalizations each year in developing countries.

Why this is critical


Story panel

  • Frequent stockouts are common in family planning supply chains, especially in developing countries, significantly impacting public health outcomes.
  • During my recent field visit to Ethiopia, stockouts were repeatedly identified by demand planners as a major barrier to effective contraceptive supply management.
  • Traditional forecasting methods fail under censorship.
  • Prior research inadequately addresses demand estimation under conditions of frequent stockouts and interruptions, often leading to biased forecasts and suboptimal inventory decisions.

The fundamental question

Key definitions


  • Stockouts: Periods when demand is higher than available inventory, leading to censored observations of demand.

  • Interruptions: Periods when no products are issued despite available stock, thus artificially recorded as zero demand.

  • Censored Demand: Demand occurring during periods when products are unavailable (stockouts or interruptions), thus not fully observable.

  • True Demand: Actual demand that would have occurred if sufficient stock was available or no interruptions happened.

Censorship scenarios

How can a demand forecasting and inventory optimization model that incorporates lost sales estimation and contextual field data enhance contraceptive supply chain performance and reduce stockouts in developing countries?

Figure 1: Censorship scenarios in family planning supply chains.

What we are going to do

How we can fill the gaps


Story panel

  • RQ1: How accurately can a Tobit Kalman Filter with conformal prediction estimate true demand under censorship?
  • RQ2: How does demand reconstruction improve inventory performance compared to baseline planning methods?
  • RQ3: How do planners adjust their orders in response to proposed model-generated recommendations?

Our proposed framework


Story panel

First stage: estimating true demand under censorship using tobit kalman filtering and conformal prediction

Story panel

First stage: estimating true demand under censorship using tobit kalman filtering and conformal prediction


Numerical experiment

Experiment setup


Synthetic data exploration - example

Actual vs. observed demand for one representative series per type × category, with disruptions and censoring shaded.

What did we find?

Overall forecasting and inventory performance across models


Method MASE (mean) Pin Ball Loss - q95 (mean) CSL (mean) Lost Sales Rate (mean) Inventory Coverage (mean)
TKF CP 0.87 47.61 0.86 0.14 5.25
Moving Average 1.06 72.65 0.82 0.18 19.6
Linear Regression 1.08 73.86 0.82 0.16 2.55
Naive 1.21 78.89 0.84 0.16 123.38

Performance evaluation - Nemenyi test

Figure 2: Average ranks of forecasting methods with 95% confidence intervals based on the Nemenyi test for all metrics. Lower ranks indicate better performance.

Performance evaluation - forecasting

Figure 3: Forecasting metrics for each series type for the different forecasting methods.

Performance evaluation - inventory

Figure 4: Inentory metrics for each series type for the different forecasting methods.

What’s NEXT

Way forward

Story panel

Develop a quantile-based inventory policy → Incorporate uncertainty directly into order decisions


Extend empirical model with external covariates → Account for special events, disruptions, and policy shifts


Conduct lab experiment with real demand planners → Measure how model recommendations affect decision-making

Materials


You can find the slides here.

Any questions or thoughts? 💬