Life expectancy at birth in Aran-Bidgol region, Iran, 2012: A study based on corrected Health Houses data

Document Type: Original Article

Authors

1 Trauma Research Center, Kashan University of Medical Sciences, Kashan, I.R. Iran

2 Epidemiology Dept., Kashan University of Medical Sciences, Kashan, I.R. Iran

3 Statistics and Information Management Dept., Kashan University of Medical Sciences, Kashan, I.R. Iran.

Abstract

Background and aims: Life expectancy is one of the most important indicators of health and well-being of a society. Since it is claimed that in Aran-Bidgol region, center of Iran, life expectancy is higher than the average of the country, this study was designed.
Methods: During a cross-sectional study, population and mortality data of Kashan University of Medical Sciences (KAUMS) in 2011 were used for calculating life expectancy. Brass Growth-Balance method was used to adjustmortality data with over 5 years old and to correct under reporting of deaths. Completeness and coverage of death registration data and the correction factor were calculated. Finally, anadjustedlife table for males and females was calculated separately. Microsoft Excel 2007 was used for calculations.
Results: Population of Aran-Bidgol was 93571 in 2012 based on KAUMS data. Among the total population, 47331 (50.6%) were males. Number of registered deaths was 479 [280 male (58.4%)]. Completeness of the death registration data was found to be %74.9 for males and %70.1 for females. Correction factor (K) for adjustment of reported death was calculated to be 1.33 and 1.42 for males and females respectively. Adjusted life expectancy at birth for males and females was 71.3 and 76.5 years respectively.
Conclusion: Although adjusted life expectancy for females in our study was to some extent more than the average life expectancy of Iranian women, but this indicator was slightly lower in men. Generally, it seems that there is no considerable difference between life expectancy of Aran-Bidgol population and national average life expectancy.

Keywords

Main Subjects


INTRODUCTION

 

Life expectancy at birth is the average number of years that a newborn is expected to live if current mortality rates continue to apply. Life expectancy at birth reflects the overall mortality level of a population. It summarizes the mortality pattern that prevails across all age groups.1,2 Life expectancy shows the level of population health overall, with the effect of death on it.3On the other hand, the life expectancy shows the final consequences of the risk factors leading to death, health programs, healthy and unhealthy behaviors of the general population and also factors affecting them quantitatively.4 It is not dependent on the age structure of a population. Therefore, it is widely used and interpreted by the public and policymakers.5 Life expectancy along with GPD per capita and the literacy rate are considered as indicators of development and the World Bank has been calculating Human Development Index on the basis of these three markers.4

Life expectancy can be estimated directly or indirectly. In the presence of enough information (population and mortality data) life tables can be constructed and it could be calculated directly. In the absence of direct access to population and mortality data, it can be calculated indirectly using statistical models. The most appropriate method of collecting data of death, which is consistent with its dynamic nature, is the registration method.6Currently, there are two sources for death registration in Iran, National Organization for Civil Registration that is legally responsible for death registration and health record system which is run by the Ministry of Health and Medical Education. A study in Iran showed that like the other developing countries, data on mortality is not complete.7

The completeness of the data on mortality by sex and age must be evaluated by the researchers before using it in health metrics.5To adjust the data for under reported deaths different methods have been introduced. Most of them need data from two consecutive censuses.8 Nevertheless, if the mortality data are available just for one year, they could be adjusted by several demographic techniques for underreporting of death.5,8 In fact, high quality data on different mortality rates will be obtained if the registry covers at least 70% of the death cases.8

It is claimed that Aran-Bidgol city alongside Kashan and Semnan in Iran have the oldest population among Iranian cities with higher life expectancy than the average of Iranian people.9 This study was designed to estimate life expectancy at birth in
Aran-Bidgol region in 2012 using the data registry of Kashan University of Medical Sciences (KAUMS) after correcting death rates for under reported deaths.

 

METHODS

After approving the study by the IRB of KAUMS and during a cross sectional study an abridged life table for Aran-Bidgolcounty was constructed in the year 2012 using vital horoscope data of Health Houses covered by KAUMS via the direct method. Brass Growth-Balance method was used to adjust over 5 years old mortality data assuming the stability of the population. This method estimates the completeness of adult death registration based on the “balancing” equation:

 

 

Where N(X) is population at each exact age,N(X+) is population at each X and above, D(X) registered death at age X, D(X+) registered death at age X and over and r is population growth rate.

Estimation of the completeness of adult death registration based on Brass Growth-Balance method has been explained elsewhere comprehensively.8 Briefly, partial birth rate (N(X)/N(X+)) against partial death rate ((Dx+)/(NX+)) was calculated and plotted, using orthogonal regression to fit the best line to the data and estimate the completeness of the death registration. Then, data points [Xi , Yi, were grouped, where Xi=D(i+)/N(i+) and Yi= N(i)/N(i+)] into 2 subsets. Subset 1 groups together points for age 5, 10, 15, 20, 25, 30. Subset 2 groups together points for ages 35, 40, 60. X1,Y1 and X2,Y2 were calculated as the average (mean) of points in subset 1 and subset 2 respectively. Finally, the correction factor, the K, was calculated using the following formula:8

 

 

At the end, the final estimate of the completeness of death registration (C) was calculated using the following formula:8

 

 

 

Mortality rates were adjusted for the incompleteness by multiplying correction factor to the reported deaths.8Microsoft Excel 2007 software was used for all calculations.

 

RESULTS

Population of Aran-Bidgol was 93571 in 2012 based on KAUMS vital registry report. Number of registered deaths based on the same registry was 479 [male 280 (58.4%)] during the same year.

 

 

Table 1: Correction of under numeration of deaths in the male population older than 5 years in Aran-Bidgol County

 

Registered

Reported

Exact

Population at

Population aged

Reported Deaths

Partial Death

Partial Birth

Age

Deaths

Population

Age

Exact age x

X and over

Over age x

Rate

Rate

x

5Dx

5Nx

x

N(x)

N(x+)

D(x+)

D(x+)/N(x+)

N(x)/N(x+)

0-4

17

4182

           

5-9

2

3455

5

764

43149

263

0.0061

0.0177

10-14

2

3378

10

683

39694

261

0.0066

0.0172

15-19

8

3588

15

697

36316

259

0.0071

0.0192

20-24

3

4643

20

823

32728

251

0.0077

0.0251

25-29

11

5351

25

999

28085

248

0.0088

0.0356

30-34

7

4482

30

983

22734

237

0.0104

0.0433

35-39

9

4025

35

851

18252

230

0.0126

0.0466

40-44

7

3601

40

763

14227

221

0.0155

0.0536

45-49

11

2618

45

622

10626

214

0.0201

0.0585

50-54

9

2117

50

474

8008

203

0.0253

0.0591

55-59

9

1690

55

381

5891

194

0.0329

0.0646

60-64

12

945

60

264

4201

185

0.0440

0.0627

65-69

18

759

65

170

3256

173

0.0531

0.0523

70-74

19

803

70

156

2497

155

0.0621

0.0626

75+

136

1694

           

 

Table 2: Correction of under numeration of deaths in the female population older than 5 years in Aran-Bidgol County, Iran, 2012

 

Registered

Reported

Exact

Population at

Population aged

Reported Deaths

Partial Death

Partial Birth

Age

Deaths

Population

Age

exact age x

x and over

over age x

Rate

Rate

x

5Dx

5Nx

x

N(x)

N(x+)

D(x+)

D(x+)/N(x+)

N(x)/N(x+)

0-4

11

3992

           

5-9

1

3157

5

715

42248

188

0.0044

0.0169

10-14

0

3331

10

649

39091

187

0.0048

0.0166

15-19

2

3606

15

694

35760

187

0.0052

0.0194

20-24

2

5220

20

883

32154

185

0.0058

0.0274

25-29

1

5257

25

1048

26934

183

0.0068

0.0389

30-34

1

4238

30

950

21677

182

0.0084

0.0438

35-39

3

3616

35

785

17439

181

0.0104

0.0450

40-44

3

3365

40

698

13823

178

0.0129

0.0505

45-49

8

2538

45

590

10458

175

0.0167

0.0564

50-54

2

2043

50

458

7920

167

0.0211

0.0578

55-59

8

1577

55

362

5877

165

0.0281

0.0616

60-64

12

954

60

253

4300

157

0.0365

0.0589

65-69

5

836

65

179

3346

145

0.0433

0.0535

70-74

13

835

70

167

2510

140

0.0558

0.0666

 

Table 3: Mean partial death and birth, and death registration coverage in Aran-Bidgol County regarding gender, 2012

Title

Male

Female

Partial death rate 5-34 yr (X1)

0.0078

0.0059

Partial death rate 40-69 yr (X2)

0.0319

0.0264

Partial birth rate 5-34 yr (Y1)

0.0263

0.0272

Partial birth rate 40-69 yr (Y2)

0.0585

0.0565

Correction factor (K)

1.33

1.42

Completeness of the death data

74.8

70.1

 

 

Among the total population, 47331 (%50.6) were males. Regarding the adjustment of death rate, the mean of partial death rate for six year age groups of 5-34 yr (X1) for male and female population were 0.0078 and 0.0059, respectively. Mean of partial birth for these 6 groups (Y1) were 0.263 and 0.0272 for males and females respectively. The mean of partial death rate for six age groups of 40-69 (X2) for males and females were 0.0319 and 0.0264 respectively. These amounts for the mean of partial birth (Y2) for these age groups were 0.0585 and 0.0565 for males and females respectively. Correction factor (K) for adjustment of under reported deaths was calculated 1.33 and 1.42 for males and females respectively. Completeness of the death registration data was found as %74.9 for males and %70.1 for females (Table 1,2,3).

Adjusted life expectancy at birth for males was 71.3 years and for females was 76.5 years (Table 4,5).

 

 

 

Table 4: Male life table for Aran-Bidgol population, Iran, 2012

Age

Years in interval

Linearity adjustment

Reported population

Deaths rate

Mortality

Probability of dying

Individuals surviving

Deaths in interval x

Years lived in interval x

Cumulative years lived

Expectancy of life at age x

x

n

a

nPx

nDx

nMx

nqx

lx

ndx

nLx

Tx

ex

0

1

0.1

889

15

0.0169

0.0166

100000

1662

98504

7130303

71.3

1-4

4

0.4

3293

2

0.0006

0.0024

98338

239

392779

7031799

71.5

5-9

5

0.5

3455

3

0.0008

0.0039

98099

378

489551

6639020

67.7

10-14

5

0.5

3378

3

0.0008

0.0039

97721

386

487641

6149469

62.9

15-19

5

0.5

3588

11

0.0030

0.0148

97335

1439

483080

5661828

58.2

20-24

5

0.5

4643

4

0.0009

0.0043

95897

413

478451

5178748

54.0

25-29

5

0.5

5351

15

0.0027

0.0136

95484

1302

474165

4700297

49.2

30-34

5

0.5

4482

9

0.0021

0.0104

94182

977

468467

4226132

44.9

35-39

5

0.5

4025

12

0.0030

0.0148

93205

1381

462570

3757665

40.3

40-44

5

0.5

3601

9

0.0026

0.0129

91823

1184

456156

3295095

35.9

45-49

5

0.5

2618

15

0.0056

0.0277

90639

2508

446925

2838939

31.3

50-54

5

0.5

2117

12

0.0057

0.0280

88131

2467

434488

2392014

27.1

55-59

5

0.5

1690

12

0.0071

0.0349

85664

2993

420837

1957526

22.9

60-64

5

0.5

945

16

0.0170

0.0814

82671

6725

396540

1536689

18.6

65-69

5

0.5

759

24

0.0317

0.1468

75945

11145

351865

1140149

15.0

70-74

5

0.5

803

25

0.0316

0.1464

64800

9489

300279

788284

12.2

75-79

5

0.5

776

48

0.0619

0.2679

55311

14815

239517

488006

8.8

80-84

5

0.5

512

46

0.0898

0.3668

40496

14855

165341

248489

6.1

+85

5

0.5

406

88

0.2167

0.7029

25641

18022

83148

83148

3.2

Table 5: Female life table for Aran-Bidgol population, Iran, 2012

Age

Years in Interval

Linearity Adjustment

Reported Population

Deaths Rate

Mortality

Probability of Dying

Individuals Surviving

Deaths in Interval x

Years Lived in Interval x

Cumulative Years Lived

Expectancy of Life at Age x

x

n

a

nPx

nDx

nMx

nqx

lx

ndx

nLx

Tx

ex

0

1

0.1

898

8

0.0089

0.0088

100000

884

99205

7654422

76.5

1-4

4

0.4

3094

3

0.0010

0.0039

99116

384

395544

7555217

76.2

5-9

5

0.5

3157

1

0.0004

0.0022

98733

219

493116

7159673

72.5

10-14

5

0.5

3331

0

0.0000

0.0000

98514

0

492569

6666557

67.7

15-19

5

0.5

3606

3

0.0008

0.0039

98514

382

491614

6173988

62.7

20-24

5

0.5

5220

3

0.0005

0.0027

98132

263

490001

5682374

57.9

25-29

5

0.5

5257

1

0.0003

0.0013

97869

130

489017

5192373

53.1

30-34

5

0.5

4238

1

0.0003

0.0017

97738

161

488288

4703356

48.1

35-39

5

0.5

3616

4

0.0012

0.0058

97577

566

486470

4215068

43.2

40-44

5

0.5

3365

4

0.0012

0.0062

97011

604

483546

3728598

38.4

45-49

5

0.5

2538

11

0.0044

0.0218

96407

2106

476771

3245053

33.7

50-54

5

0.5

2043

3

0.0014

0.0068

94301

645

469894

2768282

29.4

55-59

5

0.5

1577

11

0.0071

0.0349

93656

3271

460105

2298388

24.5

60-64

5

0.5

954

17

0.0176

0.0844

90386

7630

432853

1838283

20.3

65-69

5

0.5

836

7

0.0084

0.0410

82756

3397

405286

1405429

17.0

70-74

5

0.5

835

18

0.0218

0.1034

79359

8209

376271

1000143

12.6

75-79

5

0.5

726

48

0.0661

0.2837

71150

20184

305287

623872

8.8

80-84

5

0.5

549

46

0.0838

0.3464

50965

17654

210692

318584

6.3

+85

5

0.5

400

87

0.2175

0.7045

33312

23467

107892

107892

3.2

 

DISCUSSION

 The present study showed that life expectancy at birth in 2012 was 71.3 and 76.5 years for males and females respectively. The difference in life expectancy at birth for men and women was 5.2 years. Based on the results of the 2011 National Population and Housing Census, performed by theStatistical Center of Iran, life expectancy at birth has been 72.1 and 74.6 yr for Iranian males and females respectively.10 Meanwhile, life expectancy at birth was reported 72 yr for males and 76 yr for females by World Health Organization (WHO) in 2012.11 These statistics to some extent differ from the results of the present study. In the current study, life expectancy at birth for men was lower than WHO and Statistical Center of Iran's reports, while, it was calculated in females a higher life expectancy than the mentioned two sources. A possible explanation for this might be that different methods were used for calculating life expectancy in our study and their calculation. In the present study, the direct method was used to calculate life expectancy. In addition, under numeration of registered death was corrected using Brass Growth-Balance method. However, WHO estimates life expectancy indirectly using statistical models like the modified Logit system.12 Statistical Center of Iran also estimates life expectancy by using indirect methods.4 YazdaniCharati et al. considered changes in life expectancy of people in Sari during 2005-2010. Based on their report, the life expectancy of males and females in 2010, the nearest years to our study, were 75 and 78.01 respectively.13 Although they have used the data of health centers, the same source was used, but they did not evaluate completeness of death registration and correct under numeration of deaths. Hosseini et al. also calculated life expectancy at birth for men and women in the Bushehr province in 2011 74.91 and 75.91 respectively.14 In addition; Ahmadi A and Shojae M during an epidemiologic study estimated the life expectancy changes during 2005-2009 in CharmahalandBakhtiary province in Iran. They found that during the mentioned period, the trend in life expectancy has been increased slightly either in men or in women. In 2009, the closest year to our study, the life expectancy for men and women has been 72.14 and 75.38 respectively.15With a little difference, their results are almost consistent with our findings.

Compared to our study, they calculated life expectancy to be higher for men and lower for women in the year close to our study.14,15 The possible explanation for these differences in results may be the different methods of life expectancy calculation. Like previous studies, they also had not corrected under reported deaths. Mokhayeri et al. calculated Life expectancy at birth in Tehran in 2010 for men and women 74.6 and 78.4 years respectively.16 This difference with our results can be justified due to the use of different source of data for providing life table by them and also other socioeconomic differences between the capital and a city with small population in the margin of the desert in central Iran.

In the all mentioned studies, little difference (less than 3 yr) was found between life expectancy of men and women. However, in the current study this difference was more than 5 yr. Khoshhali M and Mahjoub H reported the life expectancy of men and women in Hamadan province to be 68.47 and 74.04 for males and females, respectively with the difference of 5.57 yr, close to our results.17 The mean gap between male and female life expectancy is about 6 yr for developed countries, while, this value is less than 2 yr for under-developed ones.18 For example, in the U.S. male life expectancy was 73.4 years for males and 80.1 years for females, a gap of 6.7 years, whereas in France it was 7.8 years and in the U.K., 5.3 years. This difference is 0.6 and 0.1 yr for India and Bangladesh, respectively.19This gap between male and female life expectancy may be explained by a number of different factors.The variety in the worldwide longevity of females indicates that the difference in mortality between the sexes depends on biological, genetic and social factors.19 Access to safe drinking water, reducing mortality, access to health facilities, as well as micronutrients, enhance literacy rate and increased proportion of women in society especially decision-making and executive positions tend to increase the life expectancy of women in developed communities.18 Mortality rateUnder-five years is very important among community development indicators because it represents important factors such as quality of life, income, culture and education of the women. Decrease in mortality rate under-five years is another effective factor that has been enhancing the life expectancy of women.According to the World Bank, in Iran, this indicator has reached from 77 to 16 over a 30 years period, 1985-2015.20

In conclusion, the current study showed more adjusted life expectancy at birth for women compared to Statistical Center of Iran and WHO reports. However, this amount was slightly lower for men compared to the numbers reported in mentioned resources. Therefore, it seems that there is no considerable difference between life expectancy of Aran-Bidgol population and the national average life expectancy.

 

CONFLICT OF INTEREST

The authors declare no conflict of interest.

 

ACKNOWLEDGEMENT

This study is a part of the PhD dissertation, supported by Deputy of Research Kashan University of Medical Sciences (Grant no: 92173). The authors also express their gratitude to the staff of Deputy of health of the university for their assistance in data gathering.

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