MORTALITY & FERTILITY

MORTALITY:

Mortality rate (word mortality comes from mortal, which originates from Latin Mors, means death) is the number of deaths (from a dieses or in general).Per thousand people and typically reported on an annually basis. It is distinct from mortality rate, which refers to the no of people who have a dieses compared to the total no of people in a population. The United Nations and World Health Organization have proposed following definition of death or mortality.

“The mortality rate is the ratio of the number of deaths during a given time period per 100,000 live births during the same period of time”.

CRUDE DEATH RATE:

Mortality study is made through the statistics of deaths occurring during a calendar year and mid year population i.e. population as on 1^st July of the year.

Crude death rate: C.D.R = D/P * 100

D=Number of deaths during a calendar year.

P=Population as on 1^st July of the year.

It expresses number of deaths per 1000 persons per year.

C.D.R is the simplest way of expressing force of mortality.  However, it fails to distinguish between population having different age structures.

INFANT MORTALITY RATE:

Infants are defined as babies who have not reached their first birth day. In terms of age they are grouped as ‘O’ year old. Infant mortality rate is defined as the ratio of number of infants deaths during a calendar year with the total number of births recorded in the same year.

I.M.R = Do/B * 100

D₀=Infants deaths during a calendar year

B=number of live births registered during the same calendar year.

       There are some patent errors present in the IMR. First types of errors are due to definitional difficulty between a “Live birth” and “Still birth”. Some babies born live but dying within few seconds after birth are classified as ‘Still born’. Second types of errors are due to the fact that babies born last year remain infants in the first  six months of the current year ,similarly babies born in the current year will remain Infants unto first six months of the coming year. Hence the cohort of Infants born (denominator) does not match properly. Simplest among them is to take data for 3 consecutive year and then to find its averages.

SPECIFIC DEATH RATES:

It has been remarked earlier that crude death rates does not take into account the age distribution of the population and thus creates errors in its interpretation, therefore specific death rates are calculated .Most common specific  death rates are                                                                                                                                 

1)      Age and sex specific death rates.  

2)      Case Fatality Death rates.

3)      Death rates by occupation or Socio Economic Status.

4)      Maternal Mortality Rate.

 For age sex specific death Rate (ASSDR) we require data of death and mid year population by age and sex groups. Numbers of Deaths in each group are divided by respective mid year population. The ASDR follow a specific curve as shown in graph:

Ages (i)	Population (Pi)	Deaths (Di)	ASDR = mi= (Di/Pi)*1000
0 - 14	16837000	288000	17.11
15 - 24	6737000	19000	2.82
25 - 39	8053000	21000	2.61
40 - 54	4848000	33500	6.91
55 - 69	2316000	38300	16.54
70 - 84	961000	56700	59.00
85+	172000	15000	87.21

             

FERTILITY:

Fertility in contrast to mortality is studied through the frequency of number of live births during calendar year in any population.

CRUDE BIRTH RATE:

The first basic index measuring Fertility is Crude Birth Rate (CBR). It is defined as the ratio of number of live births recorded in a calendar year to the mid year population of that calendar year. 

C.B.R = B/P * 1000

C.B.R is a comparable index to C.D.R However, its own definition suffers form a serious draw back .All person in denominator P are not exposed to the risk  of giving births . Hence numerator do not match together, whereas this defect is not present in CBR and CDR serves the purpose of finding rate of natural increase as the difference between them .

Rate of natural Increase =CBR-CDR.

GENERAL FERTILITY RATE (GFR):

AS a refinement to CBR a General Fertility Rate (GRF) is calculated in which denominator is mid year female population of the age group 15-49. The age group 15-49 for females is known as fertile age group, as almost all births takes places within this age group.

Hence

AGE SPECIFIC FERTILITY RATES:

As a more in-depth study of behavior of fertility in human population Age Specific Fertility rates are found with respect to ages of mothers, usually in five year age groupings 15-19.20-24… up to 45-49 for mothers. The pattern of ASFR is usually a bell shaped curve. Table shows the working of calculation of ASFR

Age of mothers	Fi (Female Population)	Bi	ASFR= (Bi/Fi)
15 - 19	850589	59537	0.069995
20 -24	784307	197023	0.251206
25 - 29	611847	181782	0.297104
30 - 34	505115	120764	0.239082
35 - 39	445275	77301	0.173603
40 - 44	367449	38252	0.104102
45 - 49	297879	13044	0.043790
Total	3862461	687703	1.178881

 ASFR can also be calculated for various subgroup of population, e.g., married, unmarried, ethnic groups, working women etc.

TOTAL FERTILITY RATE:

ASFR through gives an indication of fertility behavior in a very logical manner, however, it requires a grasp of about 7 values. Hence to abbreviate and to arrive at a one single index ASFR are summed and multiplied by size of age groups of mother (k) to yield Total Fertility Rate (TFR).