৪৯তম বিসিএস ⎯ পরিসংখ্যান [৯৮১]

Dependency ratio measures the economic pressure on the productive population. It compares those typically not in the labor force (ages 0–14 and 65+)—the dependents—to those in the working ages (15–64). A higher ratio signals more dependents relying on each working person, which can strain resources—an important socioeconomic indicator for countries like Bangladesh.

A 55% dependency ratio means that for every 100 people in the working-age group, there are 55 dependents (children and the elderly). 
This highlights the burden on the labor force. Managing such a ratio is important for Bangladesh’s economic planning and 
employment generation strategies.

Explanation: In Bangladesh, a major pattern is rural-to-urban migration, mainly driven by employment, better wages, and service facilities in cities such as Dhaka, Chittagong, and Gazipur. This internal migration is a key driver of rapid urbanization and labor supply in urban informal sectors.

Source: Bangladesh Bureau of Statistics (BBS), Internal Migration and Urbanization Survey (2015–2020)
World Bank Report: “Dynamics of Rural-Urban Migration in Bangladesh” (2019)

Explanation:
In demography, nuptiality deals with marriage-related aspects such as age at marriage, proportion of married persons, marriage rates, etc. It helps understand the social structure and reproductive potential of a population. In countries like Bangladesh, nuptiality indicators (e.g., average age at first marriage) are crucial for policymaking in health, population control, and women's empowerment.

Explanation:
NRR measures the replacement level of females in a population, considering both fertility and female mortality. অর্থাৎ, NRR বলতে বোঝায় নবজাতক কন্যাদের মধ্যে কতজন প্রজননযোগ্য বয়স ব্যাপী মানে, ৪৯ বছর পর্যন্ত বেঁচে থাকবে। An NRR of 1 means each woman is, on average, replaced by one daughter during her lifetime — implying zero population growth in the long run (under closed population conditions).

A high youth dependency ratio means a large portion of the population is under 15. Such countries must invest in education, vocational training, and new employment opportunities, so that this upcoming generation becomes productive workers. For Bangladesh, this is crucial to leverage the demographic dividend.

​Source: United Nations Population Fund (UNFPA). “State of World Population Report” (2023, Bangladesh chapter)
World Bank (2021). “Bangladesh: Tapping the Demographic Dividend.”

Explanation:
GRR counts the average number of daughters a woman would have, ignoring mortality, whereas NRR adjusts for mortality rates. If NRR is noticeably lower than GRR, it means not all daughters born survive to the end of reproductive age, pointing toward high female child or adolescent mortality.

Explanation: An index number represents a percentage change from a base year, which is typically set at 100. Therefore, an index of 120 indicates a 20% increase (120 - 100 = 20) relative to the base year. 

​Source: Business Statistics, SP Gupta, MP Gupta.

Explanation:
Fisher’s Ideal Index is called ideal because it overcomes the bias of both Laspeyres’ (base year weighted) and Paasche’s (current year weighted) indices by taking their geometric mean, satisfying time reversal and factor reversal tests.

Time reversal test- An index number formula should give consistent results over time. If we reverse the time period (swap base year and current year), the product of the two index numbers should be 1 (or 100, depending on scale).
Mathematically:
P₀₁×P₁₀=1
where, P₀₁= price index from time 0 to 1
P₁₀= price index from time 1 back to 0
Interpretation:
If an index satisfies this test, it means it is time-consistent — the upward change going forward should be exactly offset by the backward change.
Which index passes?
Fisher’s Ideal Index satisfies the time reversal test, whereas Laspeyres’ and Paasche’s indices do not, due to their fixed weighting systems.

Factor reversal test- This test checks whether the price index multiplied by the quantity index equals the value index (i.e., the change in total monetary value from base period to current period).
Mathematically:
P₀₁×Q₀₁=V₀₁
Interpretation:
If a formula passes this test, it means it measures price and quantity changes without leaving any part unexplained, perfectly decomposing the change in total value.
Which index passes?
Again, Fisher’s Ideal Index satisfies this test, while Laspeyres’ and Paasche’s indices do not.

Source: Statistics, HSC, Md. Abdul Aziz. 
S.P. Gupta, Statistical Methods, 50th Edition, 2020
M.P. Gupta, Fundamentals of Statistics, 2018

Push factors are conditions in the origin area that force people to leave—such as job scarcity, poverty, disaster, land erosion. 
Option (c) is a pull factor, attracting people towards urban areas because of better services.
push factors- lack of rural opportunities, natural disasters, land pressure
 pull factors - urban education, health facilities, factory jobs.

Explanation: NRR = Less than 1 means reduction in size over generations. 
​Here, the replacement level is less than 1, which interprets that, population will decrease.

Explanation: GFR = births per 1,000 women aged 15–49. It provides a more accurate and meaningful measure of fertility by focusing only on the segment of the population actually capable of giving birth — women of reproductive age (typically 15–49 years). It removes distortion of sex-age structure.

​Reference: Pollard, Yusuf & Pollard (1990).

Index numbers are like economic barometer. They measure the change of price, quantity, value etc. over time. They are useful in calculating Consumer price index/cost of living index. They measure relative change in variables and thus give important insights on economy. 

​Reference: Statistics, Md. Abdul Aziz (HSC). Business Statistics, SP Gupta, MP Gupta.

Explanation: More dependents imply higher expenditure on non-working population. More children = more dependents → They do not earn money, so they rely on adults for their needs. Working people have to support more children, so a greater share of income is spent on food, education, healthcare, etc.

​Reference: UN Population Division (2017), Live Mcq lecture Pdf.

Explanation: NNP is calculated from national income accounting, not index numbers directly. 
On the other hand, Index number is economic barometer which give us insights on economic conditions like inflation, relative price change over time, cost of living etc. in a country. These are useful in adjusting wages and giving new pay scale.

​Source: Business Statistics, SP MP Gupta.

ASFR considers 7 age structures (15-19,20-24, 25-29, 30-34, 35-39, 40-44, 45-49). 
​They calculate fertility rates for each age group.  
Formula of ASFR (for age group i ) = (Births of age group i / Women age group i) × 1,000 
​= (400/ 5,000) × 1,000 
​= 80. (Here, i= 20-24)

Explanation: NRR=1 indicates each generation of mothers is exactly reproducing and hence replacing itself. It interprets a population stability in the long run.
NRR<1 interprets a population decline in the long run.
NRR>1 interprets a population growth in the long run.

ASFR is calculated for specific reproductive 7 age groups (e.g. 15-19, 20–24, 25-29, 30-34, 35-39, 40-44, 45-49). 
​It refers to live births (both boy and girl) per 1,000 women in a specific age group, not female births only. 
​It is always more than GRR because GRR only considers female births.

Each measure is a refined version of the previous one: 

CBR → GFR → ASFR → TFR → GRR → NRR; They move from general to specific, becoming more accurate and meaningful for demographic analysis.

Crude Birth Rate (CBR)
    ↓ (slightly refined)
General Fertility Rate (GFR)
    ↓ (age-specific refinement)
Age-Specific Fertility Rate (ASFR)
    ↓ (sum of ASFRs)
Total Fertility Rate (TFR)
    ↓ (focuses only on female births)
Gross Reproduction Rate (GRR)
    ↓ (adjusted for female mortality)
Net Reproductive Rate

Crude death rate, 
​CDR = (Total deaths/ Total population) × 1000
​= (1,800/2,00,000) × 1,000 
​= 9

Explanation:
Population doubling time = 70 / growth rate (%)
Doubling time = 70/2
​= 35 years

Gross Reproduction Rate estimates daughters a woman will have assuming no mortality. It is more refined version than TFR. 

Explanation: Replacement-level TFR ≈ 2.1. A TFR of 1.7 is below this level, indicating a future decline in population. (Remember, GRR is roughly half of the TFR. As, GRR < 1 indicates population decline, TFR < 2.1 indicates population decline also).

​Reference: Weeks, J. R. (2015). Population: An Introduction to Concepts and Issues.

Explanation: CBR = (Births / Total population) × 1,000 
​→ Births = (25 × 80,000) / 1,000 
​= 2,000.

GRR (Gross Reproduction Rate): এটা বোঝায়, “একজন মহিলার পুরো জীবনকালে কত মেয়ে সন্তান হবার সম্ভাবনা আছে যদি বর্তমান জন্মহার (ASFR) একই থাকে।” এখানে মৃত্যুর হিসাব (mortality) নেওয়া হয় না।
NRR (Net Reproduction Rate): এটা বোঝায়, “একজন মহিলার পুরো জীবনকালে কত মেয়ে সন্তান বাঁচে এবং প্রজননযোগ্য বয়সে পৌঁছায়।” এখানে মৃত্যুর প্রভাব ধরা হয়।

যদি GRR = NRR হয়, তাহলে এর মানে হলো:
মহিলারা প্রজননযোগ্য বয়স পর্যন্ত সকলেই বেঁচে থাকে, কোনো মৃত্যু হয়নি। অর্থাৎ, নবজাতক কন্যা শিশুদের মধ্যে কেউই সন্তান ধারণে সক্ষম বয়সের শেষ সীমার অর্থাৎ 49 বছরের পূর্ব পর্যন্ত মারা যাবে না। 
GRR considers only fertility, while NRR accounts for both fertility and mortality. If GRR = NRR, mortality has no effect, meaning all women survive through their reproductive years.

Source: Statistics (HSC Level ), MA Aziz, Live MCQ class lecture and lecture slide

Net migration = In-migration – Out-migration 
​= 2,000 – 500 
​= 1,500

​1500 for 100000 people. 
​So, 1500/100 = 15 for 1000 people.

Natural Growth Rate = CBR − CDR
Here, Natural Growth Rate = (30/1000) − (10/1000) 
​= 0.03 - 0.01
​= 0.02
​= 2%

CDR uses entire population in denominator, without adjusting for age structure — hence crude. CBR also does the same. 
​That is why we use better measurement techniques like GFR, TFR etc.

Population Density = Total population ÷ Land area
Country X: 80,000,000 ÷ 200,000 = 400 persons/sq km
Country Y: 80,000,000 ÷ 800,000 = 100 persons/sq km
So, 400 is four times larger than 100, therefore Country X is much more crowded.

​Option A is correct.

We have to add all ASFRs:

0.05 + 0.21 + 0.29 + 0.19 + 0.09 + 0.03 + 0.01 = 0.87
Multiplying by 5: TFR = 0.87 × 5 = 4.35

​Interpretation: Each woman is expected to give birth to around 4 children — indicating a high fertility population.