इस ब्लॉग्स को सृजन करने में आप सभी से सादर सुझाव आमंत्रित हैं , कृपया अपने सुझाव और प्रविष्टियाँ प्रेषित करे , इसका संपूर्ण कार्य क्षेत्र विश्व ज्ञान समुदाय हैं , जो सभी प्रतियोगियों के कॅरिअर निर्माण महत्त्वपूर्ण योगदान देगा ,आप अपने सुझाव इस मेल पत्ते पर भेज सकते हैं  chandrashekhar.malav@yahoo.com
http://epgp.inflibnet.ac.in/vt/ls/infsci/obsolence_%20factors/OBSOLESCENCE%20FACTORS%20AND%20PATTERN%20OF%20LITERATURE_Etext.mp4
09. Obsolescence Factor: Definition and Calculation
P 07. Informetrics & Scientometrics *
By :I K Ravichandra Rao,Paper Coordinator
09. Obsolescence factor: Definition and Calculation
Home
Content
Content
Multiple Choice Questions
1 / 1 Points
1 / 1 Points
Question 1: Multiple Choice
Diachrounus means
 Citations to books and Journals
 Set of references/ citations of a subject from the begininning to the end
 Increasing trend of references to a subject
 Decreasing trend of references to a subject
0 / 1 Points
Diachrounus means
 Citations to books and Journals
 Set of references/ citations of a subject from the begininning to the end
 Increasing trend of references to a subject
 Decreasing trend of references to a subject
0 / 1 Points
Question 2: Multiple Choice
Higher the growth of literature higher the obsolescence as well as
 Lower the halflife
 Lower the library use
 Higher the halflife
 Higher the use of library
0 / 1 Points
Higher the growth of literature higher the obsolescence as well as
 Lower the halflife
 Lower the library use
 Higher the halflife
 Higher the use of library
0 / 1 Points
Question 3: Multiple Choice
Obsolescence is related to
 Increasing value of a product
 Decreasing value of the product
 Experience of Life
 Age of a library
1 / 1 Points
Obsolescence is related to
 Increasing value of a product
 Decreasing value of the product
 Experience of Life
 Age of a library
1 / 1 Points
Question 4: Multiple Choice
Synchronous means
 Set of references at a single point of time
 Psychological behaviour of a reader
 Decreasing use of a library
 Increasing use of Library
0 / 1 Points
Synchronous means
 Set of references at a single point of time
 Psychological behaviour of a reader
 Decreasing use of a library
 Increasing use of Library
0 / 1 Points
Question 5: Multiple Choice
The term obsolescence is derived from the ______________ word
 Greek term
 Latin
 Russian
 French
2 / 5 PointsFinal Score:
The term obsolescence is derived from the ______________ word
 Greek term
 Latin
 Russian
 French
Question 1: Matching (Simple)
Match the Columns
 (D) A. Apparent obsolescence
 (C) B. Corrected Obsolescence
 (B) C. Half Life
 (A) D. Annual Aging Factor
 A. Ratio of percentage of nonused in success years
 B. Half the use of total individual articles in a document
 C. Factor by which the active life of an individual Article on a set of documents tends to delay annually
 D. By which the active life of article in Periodicals appears to decay
0 / 1 PointsFinal Score:
Match the Columns


0 / 1 PointsFinal Score:
True or False
1 / 1 Points
1 / 1 Points
Question 1: True or False
Obsolescence is decline over time invalidity of utility of information
True
False
0 / 1 Points
Obsolescence is decline over time invalidity of utility of information
True
False
0 / 1 Points
Question 2: True or False
Weeding Policy can be derived on the basis of obsolescence factors
True
False
1 / 2 PointsFinal Score:
http://epgp.inflibnet.ac.in/vt/ls/infsci/obsolence_%20factors/OBSOLESCENCE%20FACTORS%20AND%20PATTERN%20OF%20LITERATURE_SL.mp4
Weeding Policy can be derived on the basis of obsolescence factors
True
False
1 / 2 PointsFinal Score:
http://epgp.inflibnet.ac.in/vt/ls/infsci/obsolence_%20factors/OBSOLESCENCE%20FACTORS%20AND%20PATTERN%20OF%20LITERATURE_SL.mp4
Objectives
To know the meaning, definition, and concept of obsolescence factors. To identify the methodology and steps to calculate obsolescence factors.
Summary
Theoretical framework for obsolesce factor, utility factor and halflife is explained. An attempt has been made to compute the obsolescence factors , utility factor, halflife and also it has been shon how to fit an exponential distribution function for the synchronous citation data. The analysis of citations received by two chemistry journals viz. Indian Journal of Chemistry and Asian journal of Chemistry, is discussed. It has been observed that these two journals have received 30,142 references for 3,027 articles at the rate of 9.95 references per article for 5 year data. The finding of the study are: The value Annual Ageing Factor (AAF) = "a” as calculated from the graph is found to be A A F =0.948687. The value of half life as observed from the graph is 15 years and calculated value is = 13.15865 years which is almost near to the observed value. The value of Utility factor (U) was found to be U = 19.48831 andthe value of the mean (m) is = 18.98392 which confirms the exponential nature of the distribution and also justify the correctness of the average value of ‘a’. Citation frequency distribution in chemical science journals follows exponential patter. The Corrected Obsolescence Factor (a) was found to be = 0.504389. Further it has been concluded that the obsolescence studies are helpful in discarding older materials in libraries; decisions regarding back volumes of periodicals; predicting the future use of literature; serving as a tool to measure the citable or usable documents in the field of chemical science.
1. Introduction
‘Obsolete’ generally means out of date or no longer in use. The process of becoming obsolete is known as obsolescence. It is also often referred to as ‘phenomenon of replacement.’ The term obsolescence was used for the first time by Gross and Gross in 1927. They analyzed the references in the 1926 volume of theJournal of Chemical Literature and observed that the number of references fell to onehalf in fifteen years. Obsolescence is thus a characteristic of scientific and technical literature. Thus, obsolescence means decreasing value of functional and physical assets or value of a product or facility from technological changes rather than deterioration. Every newborn grows old and eventually dies. This is universally accepted as truth. So, perplexity sets in when sometimes it is reported that "life expectancies may not always decrease as organisms grow older". It was reported in Science and quoted in the Times of India dated 30^{ th} Oct. 1992 that the results of certain experiments on fruit flies indicated that once a fly was past a certain age, its life expectancy may increase with age. Is this consistent with the universal truth stated in the first line above? Such seeming anomalies may be reconciled only through a detailed study of the phenomenon of aging.
The concept obsolescence is of obvious interest to information theoreticians who concern themselves with the development of career and librarians who administer growing collection in finite spaces. Such librarians look to research on obsolescence to help them decide which item to keep and which to store or discard in order to make room for new acquisitions. Increased periodical costs have made imperative to cancel some subscriptions and librarians have turned once again to obsolescence research in hope that the concept can be employed to forecast future as well as to describe the current or past use.
2. Meaning and Definition
Obsolescence means the decreasing value of functional and physical assets from technological change rather than deterioration. It is characterized by terminology and metaphors that link inevitable organic (aging or decay) or scientific phenomenon (half life) to the phenomenon of changing use or published literature over a period of time. In other words, obsolescence is decline in the usage of literature over a period of time. When the use of document ceases, it is termed as obsolete.
Types of Obsolescence
Actually obsolescence implies a relation between time and use but the effect of time are revealed in different ways. The impact of time on use of document can be studied in two ways: namely synchronous studies and diachrounus studies (Line, 1970). Synchronous studies are made on records of uses or references at one point in time and compress the uses against the age of distribution of the materials used or cited. With respect to obsolescence studies majority of the studies have used citations, records of consultations or loans.
In synchronous study the citations are counted back ward i.e. references in an journal articles is examined to find out how many references have been cited for that particular year. Like, year wise references are analysed. Half life annual aging factor and utility factors are studied with this type of study. The half life of journal article is the time during which half of all the currently active literature was used. The median of an age distribution in other words is half life.
In diachronous study the successive observations at different time are made by counting the citations in forward direction i.e. counting the citations that an article or journal published in 2005 is going to get in year 2006, 2007…etc. This type of study is helps in determining the rate at which the citations decline in future. Many studies have been undertaken in this field. Some of the notable studies in the field are Gros and Gross (1927), Burton and Kessler (1960), Kent and Others (1979), Jain (1966), Brookes (1970), Line (1970, 1974)Ravichandra Rao (1971), Sangam (1989), Moed (1998), Gupta (1997,1998), etc.
While studying and reviewing the studies in the field of obsolescence, it is observed that very few studies have been done. Though new indicators and methods are being developed and applied to study the obsolescence, the case studies are found to be very less. In the present study an attempt has been made to identify the obsolescence factors and pattern in the field of chemical science.
Theoretical framework for the Obsolecence factors
Burton and Kebler (1960) were the first to use the term ‘halflife’ as applied to documents in 1960. It is defined as ‘the time during which onehalf of all the currently active literature published.’ It is the period of time needed to account for onehalf all the citations received by a group of publications. The concept of halflife is always discussed in the context of diachronous studies. More precisely, Line and Sandison (1974) refer to diachronous studies in those that follow the use of particular items through successive observations at different points in time, whereas synchronous studies are concerned with the plotting the age distribution of material used at one point of time. However, there is no reason to suppose that the halflife for some subject is the same as the median citation age in that subject. Halflife in the context of synchronous data is referred to as median age of the citations / references. The use of literature may decline much faster with data of ephemeral relevance, if it is in the form of reports, thesis, advance communication or preprint and in the context of advancing technology. However, the use of literature may decline slowly when it is descriptive (e.g., taxonomic botany) and critical (e.g., literary criticism).
Brookes (1970) in one of his articles argued that if growth rates of literature and contributors are equal then the obsolescence rate remains constant. In this sense growth and obsolescence are related. Ravichandra Rao and Meera (1991) studied the relationship between growth and obsolescence of literature, particularly in mathematics. Gupta (1999) studied the relationship between growth rates and obsolescence rates and halflife of theoretical population genetics literature. He observed that the lognormal distribution fits very well to the age distribution of citations over a period of time.
In the analysis of obsolescence, Brookes (1970) argued that the geometric distribution expresses the idea that when a reference is made to particular periodical of age t years (1a) a^{t1} . ‘a (< 1)’ is a parameter – the annual aging factor; it is assumed to be constant over all values of t. Let U = 1 + a^{2} + a^{3 }+ a^{4} + …. + a^{t} + …. i.e., U = 1/(1a). Similarly if U(t) = a^{t} + a^{t+1} + a^{t+1 }+ ^{ }a^{t+2} + …… = a^{t} (U(0), then U(t)/U(0) = a^{t}. Using this relation, by graphical method, we can compute halflife as well as ‘a’. If we assume that the literature is growing exponentially at an annual rate of g, we then have R(T) = R(0)e^{gT}, where R(T) is the number of references made to the literature during the year T. We also have
U(0) = R(0)/(1a_{0}) and U(T) = R(T)/(1a_{T})
Where a_{0} and a_{T} are the annual aging factors corresponding to the years 0 and T respectively. Under the assumption that utility remains constant (U(0) = U(T)) , we have R(0)/(1a_{0}) = R(T) )/(1a_{T}). By substituting the value of R(T), we get a relationship value between the growth and the obsolescence:
e^{gT} = (1a_{T})/(1 a_{0})
However, Egghe and Ravichandra Rao (1992) showed that the obsolescence factors (aging factors) ‘a’ is not a constant, but merely a function of time. They have also shown that the function ‘a’ has a minimum which is obtained at a time t later than the time at which the maximum of the number of citations is reached.
Egghe (1993) developed a model to study the influence of growth on obsolescence. He obtained different results for the synchronous and diachronus studies. He argued that for an increase of growth implies an increase of obsolescence for the synchronous case and for the diachronous case, it is quite the opposite. In order to derive the relationship, he also assumed the exponential models for growth as well as for obsolescence. In another paper, for the diachronous aging distribution and based on a decreasing exponential model, Egghe (2000) derived first citation distribution. In his study he assumed the distribution of the total number of citations received conforms to a classical Lotka’s function (16). The first citation distribution is given by
f (t_{1}) = g (1 a ^{t1})^{a1}
where g is the fraction of papers that eventually get cited; t_{1} is the time of the citation, ‘a’ is the aging rate and a is Lotka’s exponent. Egghe and Ravichandra Rao (2002) in their study in 2002 observed that the cumulative distribution of the age of the most recent references is the dual variant of the first citation distribution. This model is different from the first citation distribution. In another study, Egghe and Rao (2001) have shown the general relation between the first citation distribution and the general citation age distribution; if Lotka’s exponent a = 2, both these distributions are the same. In the same study, they have argued that the distribution of n^{th} citation is similar to that of the first citation distribution. Egghe, Rao and Rousseau (1995) studied the influence of production on utilization function. Assuming an increasing exponential function for production and a decreasing one for aging, these authors have shown that in the synchronous case, the greater the increase in production, the greater the obsolescence; however, for the diachronous case it is quite the opposite. This proof is different from the earlier one derived by Egghe.
The study of obsolescence, in practical terms, is related to changes in the use of documents over time. Line and Sandison (1974), Jain (1966a, 1966b), Kent and others (1979) in their Pittsburgh study, and FussIer and Simon (1969) attempt to prove the hypothesis that use declines over time. Line and Sandison, however, argued that this hypothesis is to be tested first and should not be made a starting assumption. Brookes (1970) claims that the decline of use over time conforms closely to a negative exponential distribution. He hypothesizes that the number of references to an issue is a function of its age~, and he assumes the function to be a geometric distribution:
p(t) = (1a)a^{t} 0 ≤ t ≤ and 0 ≤ a ≤ 1.
p(t) is the probability mass function of reference to an issue of the journal of age tyears; if R references are made to a given periodical during its first year of life, then aR references can be expected during its second year, a^{2}R references can be expected during its third year, and so on. Under the assumption that a is constant for all values of t and for a < 1, the series a^{t} converges to the sum as t . . Therefore, the total number of references that will be made to it during its infinite life time is
U(o) =
If the periodical is t years old, then the number of further references to it can be computed by:
U(o) is called the total utility of a periodical which has just been published. Brookes (1970) suggests a graphical method for computing a. The function is called the utility factor of the periodicals. Under the assumption that the literature is growing exponentially at an annual rate of growth g, we have:
R(T) = Re^{gt}
where R(T) is the number of articles at time T and R is the number of articles at time T=O. Brookes (1970) and also Line (1970) have discussed the computational aspects of halflife, utility factor, etc. in their articles. Below a worked out example has been given in this regard.
An Worked out Example
We considered synchronous approach to collect the data for obsolescence analysis. The citation appended to the articles published in the following two journals
 Indian Journal of Experimental Biology (CSIR), New Delhi
 Asian Journal of Chemistry” New Delhi.
were considered as source data. We have collected the dta for five years (20012005). For computation of obsolescence rate, the graphical method as explained by Brookes may be used. The data is given in Table 2. Table 1 gives the summary of the data.
Below, an attempt has been made to fit the exponential distribution, to compute the ageing factor, utility factor and halflife.
Table1: Average Citation Rate of Journals
Year

Asians Journal of Chemistry

Indian Journal of Exp.Biology
 
Articles

References

Citation ate

Articles

References

Citation Rate
 
2001

276

1409

5.11

378

4735

12.53

2002

271

1583

5.66

314

4494

14.31

2003

302

1783

5.90

278

3772

13.57

2004

295

1878

6.37

297

3009

10.13

2005

351

2470

7.04

265

5059

19.09

Total

1495

9073

6.02

1534

22069

13.926

Some Observation: Out of 30142 references 38% are received for the publications of the last 10 years; 69.57% for the last two decade; 93 % for the last four decade, 99.10% citations are received for the last 6 decades and only 0.9% are for the other decades which are 269 in number. The half of the citations has been produced up to the age of 13 years (15180). Maximum number of references has been observed in the year 2000 (1562 i.e. 5.08%) followed by 1998 (1530), 1996 (1510) and 1997 (1501).This shows that scholars are using current information for their research purposes. More than 117 articles are from the age more than 71 to 105 years.
Table2: Citation Frequency Distribution of Journals
Year

Age (x)

Citations

Cumulative
Citations

Tail

% of Citations

% Cumulative Citations

2005

0

15

15

30142

0.049764

0.049764

2004

1

191

206

30127

0.633667

0.683432

2003

2

410

616

29936

1.360228

2.04366

2002

3

761

1377

29526

2.524716

4.568376

2001

4

1221

2598

28765

4.050826

8.619202

2000

5

1562

4160

27544

5.182138

13.80134

1999

6

1497

5657

25982

4.966492

18.76783

1998

7

1530

7187

24485

5.075974

23.84381

1997

8

1501

8688

22955

4.979762

28.82357

1996

9

1510

10198

21454

5.009621

33.83319

1995

10

1276

11474

19944

4.233296

38.06649

1994

11

1306

12780

18668

4.332825

42.39931

1993

12

1278

14058

17362

4.239931

46.63924

1992

13

1122

15180

16084

3.722381

50.36162

1991

14

1070

16250

14962

3.549864

53.91149

1990

15

971

17221

13892

3.221419

57.1329

1989

16

882

18103

12921

2.92615

60.05905

1988

17

757

18860

12039

2.511446

62.5705

1987

18

734

19594

11282

2.43514

65.00564

1986

19

716

20310

10548

2.375423

67.38106

1985

20

662

20972

9832

2.196271

69.57733

1984

21

723

21695

9170

2.398646

71.97598

1983

22

595

22290

8447

1.97399

73.94997

1982

23

553

22843

7852

1.834649

75.78462

1981

24

529

23372

7299

1.755026

77.53965

1980

25

475

23847

6770

1.575874

79.11552

1979

26

479

24326

6295

1.589145

80.70466

1978

27

444

24770

5816

1.473028

82.17769

1977

28

396

25166

5372

1.313781

83.49147

1976

29

333

25499

4976

1.104771

84.59624

1975

30

359

25858

4643

1.191029

85.78727

1974

31

386

26244

4284

1.280605

87.06788

1973

32

311

26555

3898

1.031783

88.09966

1972

33

272

26827

3587

0.902395

89.00206

1971

34

254

27081

3315

0.842678

89.84473

1970

35

284

27365

3061

0.942207

90.78694

1969

36

239

27604

2777

0.792914

91.57986

1968

37

230

27834

2538

0.763055

92.34291

1967

38

178

28012

2308

0.590538

92.93345

1966

39

189

28201

2130

0.627032

93.56048

1965

40

143

28344

1941

0.474421

94.0349

1964

41

135

28479

1798

0.44788

94.48278

1963

42

100

28579

1663

0.331763

94.81454

1962

43

127

28706

1563

0.421339

95.23588

1961

44

159

28865

1436

0.527503

95.76339

1960

45

91

28956

1277

0.301904

96.06529

1959

46

104

29060

1186

0.345034

96.41032

1958

47

101

29161

1082

0.335081

96.74541

1957

48

100

29261

981

0.331763

97.07717

1956

49

80

29341

881

0.26541

97.34258

1955

50

64

29405

801

0.212328

97.55491

1954

51

66

29471

737

0.218964

97.77387

1953

52

72

29543

671

0.238869

98.01274

1952

53

65

29608

599

0.215646

98.22839

1951

54

53

29661

534

0.175834

98.40422

1950

55

44

29705

481

0.145976

98.5502

1949

56

49

29754

437

0.162564

98.71276

1948

57

47

29801

388

0.155929

98.86869

1947

58

27

29828

341

0.089576

98.95826

1946

59

27

29855

314

0.089576

99.04784

1945

60

18

29873

287

0.059717

99.10756

1944

61

20

29893

269

0.066353

99.17391

1943

62

12

29905

249

0.039812

99.21372

1942

63

22

29927

237

0.072988

99.28671

1941

64

14

29941

215

0.046447

99.33316

1940

65

20

29961

201

0.066353

99.39951

1939

66

12

29973

181

0.039812

99.43932

1938

67

19

29992

169

0.063035

99.50236

1937

68

16

30008

150

0.053082

99.55544

1936

69

7

30015

134

0.023223

99.57866

1935

70

10

30025

127

0.033176

99.61184

71

117

30142

117

0.388163

100
 
Total

30142

100

Figure No. 2: Cumulative Citation frequency Distribution
Test of Exponentially of Citation Distribution
The data of column 5 of table3 are plotted as frequency polygon 'AA' in figure 3. The curve AA looks like a negative exponential distribution. The data indicates a roughly declining trend in the frequency citations as against the cited ages. The points are concentrated at one end and the curve tapers off gradually to years at the other end while an initial buildup occurs from the first entry (t = 0). With the help of table 3 the values of and σ are calculated; Mean =17.06234; Variance =159.2974; SD =12.62131; also, in order to test the exponentially of the distribution, another test i.e. KolmogorovSmirnov Test (KS Test), is applied. The observed value of cumulative citation frequencies are calculated and presented in column 6 of Table3. The calculation of the estimated values: 
F(x)=le^{ϴx } ...................(1)
Where x = 0,1,2,3,4,5,.......
and
The estimated values using (10 are presented in column 7 (represented as E(x) in Table3. To test the exponentiality of the distribution, KS test is used. According to this test, the maximum deviation in observed and estimated values, 'D' is calculated as follows: D = F(x)E_{n}(x). At the 0.01 level of significance, the KS statistics is equal to 1.63/ n^{1/2}. If 'D' is greater than KS statistics; than the distribution does not fit the theoretical distribution at this level of significance. In this case n =71, hence KS statistics for the 0.01 level should be 1.63/70^{1/2} =0.1948 and the value of 'D' should not exceed this. The examination of the data of column 6, 7 and 8 of table3 reveals that 'D' value does not exceed the 0.1948 limits, Theeta value 0.058609 and D value is 0.193445 and hence it confirms statistically that the distribution of the data follows negative exponential distribution.
Table3: Citation Frequency Distribution of Journals and Parameter values
Year

Age

Citations

%

Cumulative

F(x)

E(x)

D

x

f(x)

xf(x)

x^{2}f(x)

Observed
 
2005

0

15

0

0

0.000498

0

0.000498

2004

1

191

191

191

0.006337

0.056924

0.050588

2003

2

410

820

1640

0.013602

0.110608

0.097006

2002

3

761

2283

6849

0.025247

0.161236

0.135989

2001

4

1221

4884

19536

0.040508

0.208982

0.168474

2000

5

1562

7810

39050

0.051821

0.25401

0.202189

1999

6

1497

8982

53892

0.049665

0.296475

0.24681

1998

7

1530

10710

74970

0.05076

0.336522

0.285763

1997

8

1501

12008

96064

0.049798

0.37429

0.324493

1996

9

1510

13590

122310

0.050096

0.409908

0.359812

1995

10

1276

12760

127600

0.042333

0.443499

0.401166

1994

11

1306

14366

158026

0.043328

0.475177

0.431849

1993

12

1278

15336

184032

0.042399

0.505052

0.462653

1992

13

1122

14586

189618

0.037224

0.533227

0.496003

1991

14

1070

14980

209720

0.035499

0.559798

0.524299

1990

15

971

14565

218475

0.032214

0.584856

0.552642

1989

16

882

14112

225792

0.029261

0.608487

0.579226

1988

17

757

12869

218773

0.025114

0.630774

0.60566

1987

18

734

13212

237816

0.024351

0.651792

0.627441

1986

19

716

13604

258476

0.023754

0.671613

0.647859

1985

20

662

13240

264800

0.021963

0.690307

0.668344

1984

21

723

15183

318843

0.023986

0.707936

0.683949

1983

22

595

13090

287980

0.01974

0.724561

0.704821

1982

23

553

12719

292537

0.018346

0.74024

0.721894

1981

24

529

12696

304704

0.01755

0.755027

0.737477

1980

25

475

11875

296875

0.015759

0.768972

0.753213

1979

26

479

12454

323804

0.015891

0.782123

0.766231

1978

27

444

11988

323676

0.01473

0.794525

0.779795

1977

28

396

11088

310464

0.013138

0.806222

0.793084

1976

29

333

9657

280053

0.011048

0.817252

0.806205

1975

30

359

10770

323100

0.01191

0.827655

0.815745

1974

31

386

11966

370946

0.012806

0.837466

0.82466

1973

32

311

9952

318464

0.010318

0.846718

0.8364

1972

33

272

8976

296208

0.009024

0.855443

0.846419

1971

34

254

8636

293624

0.008427

0.863672

0.855245

1970

35

284

9940

347900

0.009422

0.871433

0.86201

1969

36

239

8604

309744

0.007929

0.878751

0.870822

1968

37

230

8510

314870

0.007631

0.885653

0.878023

1967

38

178

6764

257032

0.005905

0.892162

0.886257

1966

39

189

7371

287469

0.00627

0.898301

0.89203

1965

40

143

5720

228800

0.004744

0.90409

0.899346

1964

41

135

5535

226935

0.004479

0.90955

0.905071

1963

42

100

4200

176400

0.003318

0.914698

0.911381

1962

43

127

5461

234823

0.004213

0.919554

0.915341

1961

44

159

6996

307824

0.005275

0.924133

0.918858

1960

45

91

4095

184275

0.003019

0.928452

0.925433

1959

46

104

4784

220064

0.00345

0.932525

0.929075

1958

47

101

4747

223109

0.003351

0.936366

0.933015

1957

48

100

4800

230400

0.003318

0.939988

0.936671

1956

49

80

3920

192080

0.002654

0.943404

0.94075

1955

50

64

3200

160000

0.002123

0.946626

0.944503

1954

51

66

3366

171666

0.00219

0.949664

0.947475

1953

52

72

3744

194688

0.002389

0.95253

0.950141

1952

53

65

3445

182585

0.002156

0.955232

0.953075

1951

54

53

2862

154548

0.001758

0.95778

0.956022

1950

55

44

2420

133100

0.00146

0.960183

0.958724

1949

56

49

2744

153664

0.001626

0.96245

0.960824

1948

57

47

2679

152703

0.001559

0.964588

0.963028

1947

58

27

1566

90828

0.000896

0.966603

0.965708

1946

59

27

1593

93987

0.000896

0.968504

0.967609

1945

60

18

1080

64800

0.000597

0.970297

0.9697

1944

61

20

1220

74420

0.000664

0.971988

0.971325

1943

62

12

744

46128

0.000398

0.973583

0.973185

1942

63

22

1386

87318

0.00073

0.975086

0.974357

1941

64

14

896

57344

0.000464

0.976505

0.97604

1940

65

20

1300

84500

0.000664

0.977842

0.977179

1939

66

12

792

52272

0.000398

0.979103

0.978705

1938

67

19

1273

85291

0.00063

0.980293

0.979663

1937

68

16

1088

73984

0.000531

0.981415

0.980884

1936

69

7

483

33327

0.000232

0.982473

0.98224

1935

70

10

700

49000

0.000332

0.98347

0.983139

71

117

8307

589797

0.003882

0.984411

0.98053
 
Total

30142

514293

13576583

0.983139

i) Annual Ageing Factor (=AAF)
Based on the negative exponential function over time or obsolescence annual aging factor is the ratio of percentage of nonused (or used) documents in successive years. In case of citations this may be measured in proportion to number of citations received in library context.
The AAF = "a" has been calculated graphically, following the procedure suggested by Brookes.
The data of column 5 of table3 are plotted on semilog paper and are shown in figure 3.
 On axis 'X' (linear scale), the values of citation ages, that is, of 't'
 in years are taken, starting with the year 2005 (t = 0), as the base year, the values were taken from t = 0 to t = 71;
 On the 'Y' axis, on to left hand side, the values of cumulative citations from "Tail" that is, 30142 for 2005, are taken on log scale,
 The resultant line by joining maximum point on a straight time, 'XY' is plotted;
 For convenience sake, a parallel line to 'XY' is drawn from the point 'T' (t) =10,000; on this line T(t) for t =1 gives the value of T(l) = a^{1} = a the Annual Aging Factor;
 The value of 'a' from this line, directly reads from the graph in figure ' 28' is equal to '0.94' approximately;
 vi) The scale on the left hand is graduated to find out different values of 'a' directly from graph, from 1.0 to 0.1;
 The time 'OA' reads the values of t = 0 to t = 20; and value for 'A' on the line at the extreme right is 0.1.
 viii) Taking this value to the left hand side, another line O 'A' is drawn parallel to 'XY'.
 Similarly, the parallel lines could be drawn to head the value for the values more than 70 years.
11. It could be observed from these lines that only one straight line is not possible for the whole data. There may be a few more lines depending upon the nature of literature of a specific subject at a particular time.
The values of 'a' thus should be calculated by using the following formula:
T(t) = a^{t}
The value as read directly from the graph for t = 1, is found to be 0.94
The value of using parallel 'OA'
a^{6 }= 0.77
6 log (a) = log (0.77)
by solving this equation we get,
log a = log (0.77) /6
=  0.04356
a = e  0.957374
Therefore,
a = 0.957374
The average value of 'a' can be taken as,
a =0.94 + 0.957374 /2
= 0.948687
Therefore A A F = 0. 0948687
t= Age of Citations in Years
Figure No. 3 Semi log Curves for T (t) and t
ii) Halflife: The time calculated/ expected during which half the use of individual articles constituting a literature has been or expected to be made. The halflife can be determined from the graph in such a way that relation a^{h}= 0.5 will hold well. The value as observed from the graph is 15 years. As calculated from the above relation, h = 13.15865 years which is almost near to the observed value. The halflife for the value of 'a' of chemical science journals literature can be calculated as follows,
Log (0.948687)^{h} = log 0..5
h log 0.948687 = h log 0.5
we get the equation as
0.69315/ 0.05268
h = 13.15865
iii) Utility factor (U)
Utility factor can be calculated by using the relationship, u  1/1 a
U=l/(la)
=1/10.948
U = 19.48831
iv) Mean: The value of the mean (m) can be calculated from the value of AAF by using following formula,
1/m= log_{e} a = log_{e} 1/a and a = 0.948
log_{e} a = log_{e} 1/0.948
1/m = 0.052676
m= 18.98392
Both values (frequency table value 17.06234 and 18.98392) being almost the same, confirm the exponential nature of the distribution and also justify the correctness of the average value of 'a' and this finding proves that Citation frequency distribution in chemical science journals follows exponential pattern.
v) Corrected Obsolescence Factor (a)
The corrected obsolescence factor is the factor by which the active life of an individual article on a set of documents tends to delay annually.
It has been calculated by using the following formulae,
ά = (0.5)^{1/m} = (0.5) ^{0.052676}
ά = 0.1.037187
Um =19.4883118.98392= 0.504389
nference
 Indian J Experimental Biology has received 22069 references for 1534 articles at the average of 13.926 citations per article while Asian Journal of Chemistry has received 9073 references for 1495 articles at the average of 6.02 references per article Over all, these two journals have received 30,142 references for 3,027 articles at the rate of 9.95 references per article for 5 year data.
 The Annual Ageing Factor (AAF) = "a” as calculated from the graph is found to be A A F =0. 0948687
 The value of half life as observed from the graph is 15 years. As calculated from the above relation, h = 13.15865 years which is almost near to the observed value.
 The value of Utility factor (U) is U = 19.48831
 The value of the mean (m) is = 18.98392 which confirms the exponential nature of the distribution and also justify the correctness of the average value of ‘a’.
 Citation frequency distribution in chemical science journals follows exponential patter.
 The Corrected Obsolescence Factor (a) was found to be = 0.504389
Findings of the Obsolescence factors are useful in understanding the researchers to what extent they can go back to obtain the required published information in their particular field of interest. In the evolution of life there is a theory called “use and disuse” which means the one always in use continuous to exist where as the one which is not in use perishes gradually. Similarly in the field of literature also the publication may go on decreasing with the advancement of age.
The obsolescence studies are helpful in discarding older materials in libraries; decisions regarding back volumes of periodicals; predicting the future use of literature; serving as a tool to measure the citable or usable documents in the field of chemical science. Results of this study cannot be generalized with other subjects and subfields.
..........................................................................................................................................
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