4. SELECTED WOOD ENERGY DATA

4.1. Energy Balances in RWEDP Member-countries
4.2. Sources of Woodfuels
4.3. Woodfuels and Employment
4.4. Woodfuel Use and Value of Woodfuels
4.5. Share of Woodfuel in Total Roundwood Production
4.6. Forest and Wood Processing Residues
4.7. Agro-residues as a Source of Energy

4.1. Energy Balances in RWEDP Member-countries

The annual energy situation of a country is often presented as an energy balance which represents the total energy flow of several energy sources and products from primary production through transformation processes to final consumption, including indigenous production, import and export, transformation and distribution losses and sectoral consumption.

RWEDP recently developed an outline for a wood and biomass energy balance which can be used to present data on wood and biomass energy production, transformation and consumption for a region, country or sub-national area (RWEDP, 1995). It follows the United Nations standard energy balance as far as is possible and convenient, in order to facilitate the integration of the wood/biomass energy balance with existing (national) energy balances.

To get an overview of the use of wood and biomass energy in member countries, RWEDP compiled data from national energy balances and other data sources. The findings are presented in Table 4.1. They show that wood and biomass energy consumption is substantial in all RWEDP member-countries, so these energy sources should be accounted for in national energy balances.

Table 4.1: Consumption of conventional, wood and biomass energy in 1993-94

Unit:PJ	Total Energy	Conventional Energy	Woodfuels	Biomass Energy	Share of Woodfuels in Total	Share of Biomass in Total
Bangladesh	714	210	141	504	20%	71%
Bhutan	14	2	12	12	86%	86%
Cambodia	94	14	79	81	84%	86%
China	31,256	23,866	3,290	7,390	11%	24%
India	8,751	5,822	2,603	2,929	30%	33%
Indonesia	2,796	1,978	818	818	29%	29%
Lao PDR	47	5	42	42	89%	89%
Malaysia	994	898	93	96	9%	10%
Maldives	2	1	1	1	55%	55%
Myanmar	348	77	271	271	78%	78%
Nepal	279	23	192	256	69%	92%
Pakistan	1,984	1,066	521	918	26%	46%
Philippines	965	507	298	458	31%	47%
Sri Lanka	174	79	85	95	49%	55%
Thailand	1,837	1,352	353	485	19%	26%
Vietnam	1,076	260	423	816	39%	76%
RWEDP	51,331	36,159	9,223	15,172	18%	30%
RWEDP (without China)	20,075	12,293	5,933	7,782	30%	39%
RWEDP (without China & India)	11,324	6,471	3,330	4,853	29%	43%

Source: Estimated from data of IEA, WRI, Country data and RWEDP's Best Estimates (see Annex 1)

Some general observations on wood and biomass in energy balances are given below:

· Energy balances were only available for Bangladesh, Cambodia, China, India, Indonesia, Malaysia, Myanmar, Nepal, Pakistan, Philippines, Sri Lanka, Thailand and Vietnam. Of these, nine came from publications of the national energy department, the rest came from publications of international government and non-government organizations;

· For all countries the consumption of biomass fuels is increasing, whereas the share of biomass energy in the total energy consumption is declining for most countries and stable for some;

· Most energy balances group several biomass fuels into one or two categories. Fuelwood is included as a separate column in the energy balances of Bangladesh, Cambodia, Myanmar, Nepal, Sri Lanka, Thailand, Vietnam (without data). UN mentions primary (including fuelwood, bagasse, animal, vegetal and other waste, alcohol and biogas) and derived biomass energy (e.g. charcoal);

· None of the energy balances distinguishes between rural and urban households/areas, and large and small-scale industries. Such a distinction would be relevant for wood & biomass energy since rural households and small-scale industries are generally the main wood and biomass energy consumers;

· The data for the production and conversion of biomass energy for all energy balances are derived from the consumption data using a standard conversion efficiency. This is suggested by the fact that none of the energy balances accounts for distribution losses or statistical differences for biomass fuels;

· The commercial sector is often grouped with the residential sector in most energy balances. Where the two sectors are distinguished the biomass energy consumption of the commercial sector is usually very low. This may be due to a lack of data and the difficulty of distinguishing the consumption of the commercial sector from that of the residential sector rather than the low consumption of biomass fuels as such;

· Data from different sources are rarely consistent, for both conventional and biomass energy.

This overview does not pretend to be complete. There may be other sources of energy data and balances that RWEDP is not aware of, so we would like to encourage national energy agencies and others to provide these data.

4.2. Sources of Woodfuels

The 'gap-theory', often quoted in the past and used to justify action in the field of enhancing forest resources as well as wood energy conservation programmes, was based on the belief that most, if not all, woodfuels originated from forests. The 'gap' between demand and supply was then used to calculate how long it would take before all the forests would disappear due to woodfuel use. However, 10-15 years of in-depth studies have shown that non-forest areas supply considerable amounts of woodfuels. In fact, evidence, albeit sketchy, shows that in many countries a major part, often over 50%, of woodfuels is derived from non-forest areas. The latter include village lands, agricultural land, agricultural crop plantations (rubber, coconut, etc.), homesteads, trees along roads, etc. Table 4.2 gives a brief overview of the sources of woodfuels in some RWEDP member-countries.

Table 4.2 - Indicative sources of fuelwood used in various RWEDP member-countries for household (HH) and industrial (Ind.) use as % of total amount used

Country	Year and Sector	million tons	Forest land 1	Other land 2	Public land 3	Unknown
Bangladesh 4	1981, HH and Ind.	5.5	13	87	-	-
India 5	1996, HH	162	51	49	-	-
Indonesia 6	1989, Urban HH	0.5-1.0	6	65	-	-29
Nepal 7	1995/96, HH	6.9	73	27	-	-
Pakistan 8	1991, HH	29.4	12.6	84.1	-	3.3
Philippines 9	1989, HH	18.3	13.7	86.3		-
Sri Lanka 10	1993, HH and Ind.	9.2	11	75	-	14
Thailand 11	1992, Rural HH	5.74	-	56	37	7

¹ Forest land includes forest plantations as well
² Other land is mainly own land, neighbours land, common land
³ Public land may include forest
⁴ Government of Bangladesh, 1987
⁵ Ministry of Environment & Forests, 1996
⁶ World Bank/ESMAP, 1990
⁷ WECS, 1997
⁸ World Bank/ESMAP and UNDP, 1991
⁹ World Bank/ESMAP, 1991
¹⁰ Ministry of Agriculture, Lands and Forestry, 1995
¹¹ RFD, 1993

4.3. Woodfuels and Employment

Although a large proportion of the woodfuels are gathered by the users themselves, the woodfuel trade is also important, particularly for urban areas and for industrial consumption.

The figures given in Table 4.3 for the woodfuels are probably based on large® scale operations only - evidence from rapid rural appraisals suggests that small scale producers in rural areas collect 20-80 kg. per day. Transporting and retailing this amount may take another day depending on area, means of transport and distance to the market. Using these average figures for small scale rural producers, the employment figure for woodfuels is probably 10 times higher than shown in Table 4.3.

Table 4.3 - Estimated employment by fuel type

Fuel type	Tons of Fuel per Tera Joule (TJ)	Estimated Employment per TJ Energy Consumed in Person Days 1
Kerosene 2	29 Kilo Litre	10
LPG 2	22 Tons	10-20
Coal 3	43 Tons	20-40
Electricity 4	228 MWh	80-110
Fuelwood 5	62 Tons	110-170
Charcoal 5	33 Tons	200-350

Source: World Bank/ESMAP, 1991

¹ Where applicable employment covers growing, extraction, production, transmission, maintenance, distribution and sales, including reading meters. It excludes employment generated outside the country for fuels that are imported in semi-finished or finished state.

² This assumes that crude oil (for refining), kerosene and LPG are imported.

³ Varying according to capital intensity of the mine, seam thickness, energy value of the coal as well as the distance from demand centres.

⁴ Varies according to production method ranging from hydro to traditional oil/coal fired units and the efficiency of electricity generation, transmission and distribution.

⁵ Depending on productivity of the site, efficiency of producers and distance from the market.

4.4. Woodfuel Use and Value of Woodfuels

Although the domestic sector accounts for the lion's share of woodfuel use in most countries, many other users such as industries are also dependent on woodfuels. Much of this use is in the informal sector for which very little information is available and for that reason the industrial consumption is in many cases under-reported. Experience has shown that in most developing countries the industrial sector accounts for 10-30% of all woodfuel use. Table 4.4, however, indicates that industrial fuelwood use would account for only approximately 3% of all woodfuel use. The same statement of under-reporting may be true to a certain extent for the domestic sector, as woodfuel consumption is often based on estimates of average per capita consumption figures. Table 4.4, which shows fuelwood and charcoal use in the domestic and industrial sectors, has been drawn up on the basis of data contained in national energy balances as published by the member-countries, as well as on the basis of additional sources of information.

Table 4.4 gives an indication of the amounts used in the domestic and industrial sectors expressed in '000 tons of oil equivalent or ktoe (1,000 ton oil equivalent, or 1 ktoe equals about 2,766 tons of wood or about 4,600 cubic metres of wood at 600 kg per cubic metre).

The value of woodfuels consumed has been estimated by using average calorific values of woodfuels as well as fuelwood and charcoal prices from FAO forestry statistics. This calculation shows that the estimated value of the recorded woodfuel use in the 15 RWEDP member-countries reaches a staggering 29 billion US dollars per year. This value is expected to be even larger due to under-reporting of woodfuel use in many countries. Furthermore, the result does not account for the social value of fuelwood supply activities.

Table 4.4 - Energy consumption in RWEDP member-countries calculated in petajoules (PJ) from information contained in National Energy Balances etc.

Country	Fuelwood			Charcoal			Year
	Domestic	Industrial	Total	Domestic	Industrial	Total
Bangladesh 1	95.76	18.93	114.69	0	0	0	1989/90
Bhutan 2	12.25	0.99	13.80	0	0.37	0.37	1988/89
China 3	3,495,00	0	3,495.00	0	0	0	1990
India 4	3,165.00	240.00	3,405.00	0	0	0	1991
Indonesia 5	868.76	0	868.76	0	0	0	1992
Lao PDR 6	32.83	0	32.83	0	0	0	1990
Malaysia 7	11.79	0	11.79	5.69	0	5.69	1992
Maldives 8	1.05	0	1.05	0	0	0	1987
Myanmar 9	342.87	0	342.87	24.65	0	24.65	1990
Nepal 10	169.30	6.43	175.73	0	0	0	1994/95
Pakistan 11	493.85	0	494.10	0	0	0	1993/94
Philippines 12	231.74	0	231.74	56.98	0	56.98	1992
Sri Lanka 13	136.12	0	163.34	0	0	0.54	1992
Thailand 14	161.93	0	161.93	185,01	0	185.01	1994
Vietnam 15	395.54	0	427.12	15.44	0.08	16.10	1990
RWEDP	9,613.78	266.35	9,939.75	287.76	0.45	289.33
% of Total	93.98	2.60	97,17	2.81	0.00	2.83

¹ Habib, A., 1994
² Ministry of Agriculture, 1991
³ ESCAP, 1991
⁴ Ravindranath and Hall, 1995
⁵ AEEMTRC, 1994
⁶ REDP, 1989a
⁷ AEEMTRC, 1994
⁸ REDP, 1989b
⁹ World Bank, 1991
¹⁰ WECS, 1996c
¹¹ Asian Energy News, 1995
¹² AEEMTRC, 1994
¹³ Ministry of Power and Energy, 1995
¹⁴ DEDP, 1995
¹⁵ World Bank/ESMAP, 1994

In order to put the value of woodfuels in perspective, various comparisons can be made. One example is a comparison between the estimated woodfuel value and the value of energy imports. In the case of Thailand, where woodfuels account for less than 30% of all energy use, the value of woodfuels is estimated to be about 2 billion US dollars which is more than 50% of the 1994 energy import bill of 95.5 billion baht (about 3.8 billion US dollars). If woodfuels were to be substituted by kerosene in Thailand the import bill would rise considerably. Using average data for stove efficiencies, heating values and oil prices, it can be shown that the energy import bill of Thailand would rise by about 850 million US dollars. Even though this amount is high, it is considerably lower than the woodfuel value. The difference is caused by the better end-use efficiency of kerosene stoves.

Comparing the value of woodfuel with the export earnings in each country in the same period is also instructive. An overview is shown in Table 4.5 and Figure 2. More recent figures are not yet available, but they are likely to lead to the same conclusions. For those countries where woodfuels are an important source of energy, it is clear that substituting woodfuels by kerosene would be difficult if not impossible, as a large part of their export earnings would be required to pay for the import of kerosene.

Table 4.5 - Woodfuel values in million US$ using average woodfuel prices (1990)

Country	Fuelwood	Charcoal	DOM. FW	Dom Char	Ind FW	Ind Char	Total
Bangladesh	306	-	255	-	50		306
Bhutan	37	3	33	-	3	3	40
China	9,320	-	9,320	-	-	-	9,320
India	9,080	-	8,440	-	640	-	9,080
Indonesia	2,317	-	2,317	-	-	-	2,317
Laos	88	-	88	-	-	-	88
Malaysia	31	49	31	49	-	-	80
Maldives	3	-	3	-	-	-	3
Myanmar	914	213	914	213	-	-	1,127
Nepal	469	-	451	-	17	-	469
Pakistan	1,318	-	1,317	-		-	1,318
Philippines	618	491	618	491	-	-	1,109
Sri Lanka	436	5	363	-	-	-	440
Thailand	432	1,595	432	1,595	-	-	2,027
Vietnam	1.139	139	1.055	133	-	1	1.278
RWEDP	26,506	2,494	25,637	2,481	710	4	29,000
Fuel prices in	US$/Ton	US$/GJ	End-use efficiencies of stoves			Fuel heating value GJ/Ton
Fuelwood	40	2.67	Fuelwood	20 %		Fuelwood	15 GJ/Ton
Charcoal	250	8.62	Charcoal	30 %		Charcoal	29 GJ/Ton

Figure 2 - Value of woodfuels as % of 1990 export earnings

4.5. Share of Woodfuel in Total Roundwood Production

The data for the total roundwood and woodfuel production in 1995, shown in table 4.6 and Figure 3, are derived from the FAOSTAT data base. This shows an extremely high proportion of woodfuel in total roundwood production in the fifteen member-countries of RWEDP in Asia. Their combined roundwood production in 1995 was about 1,075 million m³, out of which about 865 million m³ (or 80%) was accounted for by woodfuel. Although China and Thailand also imported roundwood, approximately 6.5 and 2.0 million m³ respectively, followed by India and Philippines (both less than 1.0 million m³) others did not import at all. This high share of woodfuel in total roundwood production is a clear manifestation of their heavy reliance on fuelwood and charcoal for energy. The share of fuelwood and charcoal (woodfuel) in total roundwood production is low (22%) only in Malaysia, which is at par with the most developed countries in Europe. In all other countries its share is 68% (China) or more, and is as high as 98% in Bangladesh. For comparison, the share of fuelwood and charcoal in total roundwood production in North and Central America, South America, Europe and Asia comprise 21%, 67%, 16% and 76% respectively.

RAP publication no. 1995/22, "Selected Indicators of Food and Agriculture Development in Asia-Pacific Region, 1984-94", published by FAO, Bangkok does not show a decline in the average annual growth rate of fuelwood and charcoal production in any of the RWEDP member-countries (FAO, 1995a). As a matter of fact, it is still growing everywhere, averaging between 1.9% and 1.4% in rapidly industrializing countries like Indonesia and Thailand, and at a growth rate not less than 2%, annually in others. On the other hand, industrial roundwood production in Bangladesh, Bhutan, Philippines, Sri Lanka and Thailand has declined at an average annual growth rate of -4.5%, -8.1%, -6.2%, -0.5% and -5.5% respectively, between 1983 and 1993.

Table 4.6 - Forest and plantation area, roundwood and woodfuel production in RWEDP member-countries

	Total Land Area (1000 ha)	Total Forest Area 1995 (1000 ha)	Natural Forest Area 1995 (1000 ha)	Plantation Area 1995 (1000 ha)	Roundwood Production in 1995 (1000 CUM)	Woodfuel Production in 1995 (1000 CUM)	Share of Woodfuel in Total Roundwood Production (%)
Bangladesh	13,017	1,010	700	310	32,044	31,310	98
Bhutan	4,700	2,756	2,748	8	1,399	1,354	97
Cambodia	17,652	9,830	9,823	7	7,765	6,725	87
China	932,641	133,323	99,523	33,800	300,360	204,059	68
India	297,319	65,005	50,385	14,620	299,163	274,272	92
Indonesia	181,157	109,791	103,666	6,125	185,895	151,228	81
Lao PDR	23,080	12,435	12,431	4	5,508	4,511	82
Malaysia	32,855	15,471	15,371	100	45,573	9,819	22
Maldives	30	-	-	-	-	-
Myanmar	65,755	27,151	26,875	276	23,281	20,450	88
Nepal	14,300	4,822	4,766	56	20,822	20,202	97
Pakistan	77,088	1,748	1,580	168	29,665	28,116	95
Philippines	29,817	6,766	6,563	203	39,857	36,540	92
Sri Lanka	6,463	1,796	1,657	139	9,625	8,925	93
Thailand	51,089	11,630	11,101	529	39,288	36,502	93
Vietnam	32,549	9,117	7,647	1,470	34,913	30,470	87
Total	1,779,512	412,651	354,836	57,815	1,075,157	864,483	80

Source: Area data from FAO, State of the World's Forests 1997; Production data from FAO Forestry Data Base

It has increased significantly in Lao PDR and Pakistan by 8.8% and 11.9% respectively. In Indonesia and Malaysia it has increased moderately, 3.9% and 4.1% respectively, and in the remaining countries the growth has been only marginal, from 0.7% to less than 3%. Although most countries in the region have been progressing rapidly in terms of their economic growth in recent years, their use of fuelwood and charcoal for energy has not declined in absolute terms over the years. The domestic sector is the greatest user of wood energy for cooking, space heating and agro-processing, primarily in rural areas. Infrastructure, availability and affordability of substitute fuels, local social cultural practices, income and living standards of users, government policy related to energy, etc. all, seem to play an important role in the selection of fuel by households for meeting their basic energy needs.

Figure 3 - Share of woodfuel in total wood production, 1995

4.6. Forest and Wood Processing Residues

Sawn wood is normally produced from logs. However, the process of conversion from trees in the forest to logs and subsequently to sawn wood is associated with waste. This waste can be in various forms such as logging waste (branches, stumps, etc.) as well as other processing waste. The following provides a brief overview of the amounts of waste generated from trees in the forest to kiln-dried sawn wood ready to be used. It should be noted that average figures are shown here and that variations in the amount of wastes generated are common, depending on methods used, etc.

When cutting trees in the forests, recovery rates vary considerable depending on local conditions. A 50/50 ratio is often found in the literature i.e. for every cubic metre of log removed, a cubic metre of waste remains in the forest (including the less commercial species). Where logging is carried out for export purposes, values of up to 2 cubic metres of residues for every cubic metre of log extracted may be valid (Adams, M., 1995). Other sources (Government of Indonesia, 1990) give a ratio of 60/40 i.e. 6 cubic metres of logs versus 4 cubic meters of waste remaining in the forests. The 40% consists of: 12% stemwood (above first branch), 13.4% branch wood, 9.4% natural defects, 1.8% stemwood below first branching, 1.3% felling damage, 1.6% stump wood and 0.5% other losses. Figures of 30% logging wastes have been reported from Malaysia (FRIM, 1992) but others (Jalaluddin et al, 1984) indicate a recovery rate of 66% with 34% being residues consisting of stumps, branches, leaves, defect logs, offsets and sawdust. This figure may be higher if unwanted species intentionally or accidentally felled are considered as well. Most of the wood residues are left in the forest to rot, particularly in sparsely populated areas where the demand for woodfuels is low.

Once the log has been produced, it is transported out of the forest for further processing such as in a saw mill where it is converted into sawn wood. Recovery rates vary again with local practices as well as species (FE, 1990). After receiving the logs, about 12% goes to waste in the form of bark. Slabs, edgings and trimmings amount to about 34% while sawdust constitutes another 12% of the log input. After kiln drying the wood, further processing may take place resulting in another 8% waste (of log input) in the form of sawdust and trim end (2%) and planer shavings (6%).

In brief, as is shown in Figure 4, an estimated 80% of the trees in the forest goes to waste while only about 20% of the original tree in the forest ends up in the form of kiln dried sawn wood.

Figure 4 - From standing tree to kiln-dried sawn wood

4.7. Agro-residues as a Source of Energy

Every year large quantities of ago-residues are generated, which are an important source of energy for domestic and industrial purposes, e.g. between 10% and 50% of all rural energy. The use of residues as a fuel puts pressure on the resource base. In order to judge the impact of increased use, an overview of the potential supply and demand should be prepared. A distinction should be made with regard to location. Ago-residues are generated either in the field where the crops are grown (straw and stalks) or at processing centres (husks of grain, shells, etc.). The field-based residues are difficult to collect and therefore often left to be burnt where they are. The process-based residues are used more extensively as a source of energy.

Ago-residues are used for many purposes, notably, the 'six F's': Fuel, Fodder, Fertilizer, Fibre, Feedstock and Further uses. The last F comprises for instance soil conditioning (coconut coir dust to retain moisture in the soil), use as a growing medium (straw for mushroom, coconut husks for orchids), packing materials, etc. Residues may even have multi-purpose uses: rice husk can be burnt as Fuel and the ash used by the steel industry as a source of carbon and as an insulator (Feedstock/Further); rice straw can be used as animal bedding (Fibre or Further) and subsequently as part of compost (Fertilizer); crop waste can be used as a Feedstock for biogas generation (Fuel) and the sludge as Fertilizer, etc.

It is unwise to assume that residues are wastes and therefore by definition more or less 'free'. Even where residues are at present freely available, they are likely, sooner rather than later, to acquire a monetary value. For instance:

· About 15 years ago rice mill owners in Indonesia gave away rice husks free of charge to truck drivers and brick makers, and would even provide free labour to load it. Once a market had developed brick makers had to pay for the husks and for labour to load the husks.

· The increased use of rice husk as a boiler fuel in the Nepali carpet industry resulted in a tenfold increase in the price from 2 to 20 NRs (about 0.04 -0.40 US$) per bag of 20 kg over a period of only 14 months.

The wastes may also be used for various purposes in the local community without direct monetary value. Such situations are not always apparent to an outsider. In common share-cropping systems the crop as well as the residues are divided between the landowner and the tiller. Also, landless people have access to residues on common lands, and sometimes may collect residues from other peoples' lands. Trying to use these residues without compensation is likely to create problems. Even in cases where money changes hands, payments may be made to some other person than to whom the original benefit accrued, which may lead to social disruptions in the community. Further factors to be considered in addition to competing use are: seasonality with large quantities available immediately after the harvest; ownership and access; fraction which can be recovered economically or in terms of the environment.

In order to estimate the amount of residues generated, use is often made of 'Residue to Crop-production' (RCR) or 'Residue to Area-planted' (RAR) ratios. Both ratios can be applied for both field and process-based residues, but RCR is most commonly used for statistical purposes because it is often more reliable than RAR (due to multiple crops per year, inter-cropping, etc.). However, RCR values can vary to a great extent (possibly even from year to year) depending on several factors, like variations in weather conditions, crop variety, water availability, soil fertility, farming practices, etc. Although for most crops general RCR data are available, in many cases the moisture content of residues is not given. This makes calculating the amount of residues based on crop production tricky. The following example demonstrates the risks of using RCR:

Rice straw: RCRs in the range of 0.416 to 3.96 have been cited in various references. The lowest amongst the values, 0.416 reported by AIT and EEC (1983), and 0.452 by Bhattacharya, S.C. and Shresta, R.M. (1990), are based on the practice of harvesting rice in parts of Thailand and other Southeast Asian countries where only the top portion of the rice stem along with 3-5 leaves is cut, leaving the remainder in the field. Where the rice is cut at about 2" above ground, the RCR becomes 1.757 (m.c. 12.71%) as reported by Bhattacharya, S.C. et al (1990). Vimal, O.P. (1979) indicates an RCR of 1.875 based on Indian experience while in Bangladesh a value of 2.858 has been reported (Government of Bangladesh, 1987) which however may be valid only for a local variety (floating rice).

Data for rice straw as presented in Table 4.7 show large variations. Due care should be taken in using RAR and RCR values to calculate the amount of residues generated in a certain area or period. Field checking should determine the most appropriate value for a given situation.

Table 4.7 - Some Residues-to-Crop Ratios (RCR) for Rice Straw

Reference	RCR	Moisture content in %	C %	N %	LHV MJ/Kg.	Ash %
Webb, B., 1979	2.60-3.96	10-12				12.7-21.4
Vimal, O.P., 1979	1.88
AIT and EEC, 1983	0.42	27			15.10	16.98
Government of Bangladesh 1987	2.86
Barnard, G., et al., 1985	1.40-2.90
Strehler, A. and Stutzle, W., 1987	1.40	12-22	41.44	0.67	10.9	17.4
Bhattacharya, S.C., et al., 1990	0.452	12.71	24.79		16.02	21.05
Massaquoi, J.G.M,, 1990	1.10-3.00
Ishaque, M. and Chahal, D.S., 1991	1.40
Ryan, P. and Openshaw, K., 1991	1.10-2.90					18-19
Kristoferson, L.A. and Bokalders, V., 1991	1.10-2.90
Bhattacharya, S.C. et al, 1990	1.757	12.71	39.84		16.02