Modelled scenario — not observed data. Not suitable as a verified count of babies born to B40/M40/T20 families.
1. Step 1 — Income-adjusted fertility index
Fertility index for an income group = ( that group's average monthly household income ÷ 10,000 ) raised to the power of −0.108027
The fertility index is a modelled value for each income group. The group average monthly household income is in RM. −0.108027 is the income coefficient from Zulqarnain & Md Yusuf (2022). RM10,000 is the reference income used for scaling.
| Income group | Representative mean income | Calculated index |
|---|---|---|
| B40 (D1–D4) | RM3,814/month | 1.10974 |
| M40 (D5–D8) | RM8,744/month | 1.01460 |
| T20 (D9–D10) | RM20,662/month | 0.92460 |
Incomes are DOSM 2024 Household Income Survey representative means.
2. Step 2 — Apply assumed group shares
Raw weight for an income group = assumed household share of that group × its fertility index
The assumed household share is used as a proxy for the distribution of mothers (40% / 40% / 20%), because matched data on reproductive-age women by income group are not available.
| Group | Assumed share | Raw weight |
|---|---|---|
| B40 | 40% | 0.443897 |
| M40 | 40% | 0.405842 |
| T20 | 20% | 0.184920 |
3. Step 3 — Convert weights to birth estimates
Normalised share for an income group = its raw weight ÷ (sum of all three groups' raw weights)
Estimated births for an income group = 414,918 × its normalised share
Malaysia's official 2024 live-birth total is 414,918 (OpenDOSM / National Registration Department). Counts are largest-remainder rounded to sum to the total.
| Group | Modelled share | Estimated births |
|---|---|---|
| B40 | 42.90% | 178,011 |
| M40 | 39.22% | 162,751 |
| T20 | 17.87% | 74,156 |
| Total | 100% | 414,918 |
4. Sources
- DOSM — Household Income Survey 2024: mean household incomes RM3,814 / RM8,744 / RM20,662. PDF report.
- OpenDOSM — Annual live births: 414,918 registered live births in 2024. Dataset.
- Zulqarnain & Md Yusuf (2022): income coefficient −0.108027 (p=0.0018), ARDL, national data 1982–2019, income variable = adjusted net national income per capita. Study (PDF).
5. Key limitations
- The study did not estimate separate fertility rates for B40/M40/T20 households. Adapting its coefficient into a power formula is our modelling choice, not a validated equation for these groups.
- The 40/40/20 shares are proxies for mothers; not verified as the distribution of women of reproductive age.
- 178,011 B40 births is an exploratory allocation, not a measured or verified count.
- Until household-level data linking mothers' income group to birth outcomes exist, present this under "Modelled scenario — not observed data".