In the scientific study of the faculty of language,M.Hauser,N.Chomsky & T.Fitch have proposed the recursion-only hypothesis in the context of biological evolution,while R.Jackendoff & S.Pinker have put forward...In the scientific study of the faculty of language,M.Hauser,N.Chomsky & T.Fitch have proposed the recursion-only hypothesis in the context of biological evolution,while R.Jackendoff & S.Pinker have put forward a strong refutation---the language-as-adaptation hypothesis.This paper briefly introduces HCF hypothesis,meanwhile examines PJ's critical comment,and finally attempts to comment on both hypothesis with a balanced view.展开更多
This paper indicates the problem of the famous Riemann hypothesis (RH), which has been well-verified by a definite answering method using a Bose-Einstein Condensate (BEC) phase. We adopt mathematical induction, mappin...This paper indicates the problem of the famous Riemann hypothesis (RH), which has been well-verified by a definite answering method using a Bose-Einstein Condensate (BEC) phase. We adopt mathematical induction, mappings, and laser photons governed by electromagnetically induced transparency (EIT) to examine the existence of the RH. In considering the well-developed as Riemann zeta function, we find that the existence of RH has a corrected and self-consistent solution. Specifically, there is the only one pole at s = 1 on the complex plane for Riemann’s functions, which generalizes to all non-trivial zeros while s > 1. The essential solution is based on the BEC phases and on the nature of the laser photon(s). This work also incorporates Heisenberg commutators [ x^,p^]=1/2in the field of quantum mechanics. We found that a satisfactory solution for the RH would be incomplete without the formalism of Heisenberg commutators, BEC phases, and EIT effects. Ultimately, we propose the application of qubits in connection with the RH.展开更多
The Porter Hypothesis,proposed by Michael E.Porter,suggests that stringent environmental regulations can enhance corporate innovation and competitiveness,challenging the traditional view that regulations increase busi...The Porter Hypothesis,proposed by Michael E.Porter,suggests that stringent environmental regulations can enhance corporate innovation and competitiveness,challenging the traditional view that regulations increase business costs.It argues that regulations motivate firms to innovate,leading to improved productivity,cost reductions,and new market opportunities.However,there are proponents and critics in academia regarding the hypothesis.Supporters claim regulations change corporate behavior,reducing agency costs and boosting research and development.Critics argue that if win-win situations exist,businesses would naturally pursue them without regulatory incentives.Key challenges in proving or refuting the hypothesis include its various versions,the difficulty in quantifying innovation and competitiveness,the complex interplay between regulation,innovation,and competitiveness,and the varying impacts across industries and regions.Additionally,the effects may require a long time to manifest,and the hypothesis’s applicability is influenced by evolving environmental policies and market environments.Despite mixed empirical findings,the Porter Hypothesis provides a valuable framework for understanding the relationships among environmental regulation,innovation,and competitiveness,but its validation requires a more comprehensive assessment.展开更多
In light of the rising evidence of the association between viral and bacterial infections and neurodegeneration,we aimed at revisiting the infectious hypothesis of Alzheimer’s disease and analyzing the possible impli...In light of the rising evidence of the association between viral and bacterial infections and neurodegeneration,we aimed at revisiting the infectious hypothesis of Alzheimer’s disease and analyzing the possible implications of COVID-19 neurological sequelae in long-term neurodegeneration.We wondered how SARS-CoV-2 could be related to the amyloid-βcascade and how it could lead to the pathological hallmarks of the disease.We also predict a paradigm change in clinical medicine,which now has a great opportunity to conduct prospective surveillance of cognitive sequelae and progression to dementia in people who suffered severe infections together with other risk factors for Alzheimer’s disease.展开更多
Soil liquefaction is one of the complex research topics in geotechnical engineering and engineering geology. Especially after the 1964 Niigata earthquake (Japan) induced many soil liquefaction incidents, a variety of ...Soil liquefaction is one of the complex research topics in geotechnical engineering and engineering geology. Especially after the 1964 Niigata earthquake (Japan) induced many soil liquefaction incidents, a variety of soil liquefaction studies were conducted and reported, including the liquefaction potential assessment methods utilizing the shear wave velocity (V<sub>s</sub>) or SPT-N profiles (SPT: standard penetration test). This study used the V<sub>s</sub> and SPT methods recommended by the National Center for Earthquake Engineering Research (NCEER) to examine which is more conservative according to the assessment results on 41 liquefiable soil layers at sites in two major cities in Taiwan. Statistical hypothesis testing was used to make the analysis more quantitative and objective. Based on three sets of hypothesis tests, it shows that the hypothesis—the SPT method is more conservative than the V<sub>s</sub> method—was not rejected on a 5% level of significance.展开更多
Aiming at gradually developing and perfecting the task-based teaching method, the essay, with enlightment from the Krashen's Input Hypothesis, discusses some issues about input, output, activities and teacher's role...Aiming at gradually developing and perfecting the task-based teaching method, the essay, with enlightment from the Krashen's Input Hypothesis, discusses some issues about input, output, activities and teacher's role in this method.展开更多
Aim To study the rules governing pressure distribution of traveling charge under the condition of Lagrange hypothesis. Methods\ The study is based on the laws of conservation of momentum and energy. Results\ The gas ...Aim To study the rules governing pressure distribution of traveling charge under the condition of Lagrange hypothesis. Methods\ The study is based on the laws of conservation of momentum and energy. Results\ The gas flow velocity distribution formula at the back of a projectile and the momentum equation of a traveling charge are deduced, and rules governing their pressure distribution under the Lagrange hypothesis conditions are established. The pressure distribution of a traveling charge is compared with that of a conventional charge. Conclusion\ The pressure distribution in the bore of a traveling charge can be accurately predicted. A parabolic pressure distribution type is revealed.展开更多
Sapir-Whorf hypothesis has its implication in translation studies. Each language is a peculiar whole. It is a product, even an expression, of the spiritual personality and the cultural particularity. Translation is a ...Sapir-Whorf hypothesis has its implication in translation studies. Each language is a peculiar whole. It is a product, even an expression, of the spiritual personality and the cultural particularity. Translation is a kind of interlingual and intercultural communication. It involves not only the transference from one language into another, but a whole set of extra-linguistic criteria. In translating we are always crossing a greater or lesser barrier or divide.展开更多
“Sapir-Whorf hypothesis"holds that human thoughts are shaped by their native languages,and speakers of different languages think differently relevantly.The hypothesis is controversial partly because it seems to ...“Sapir-Whorf hypothesis"holds that human thoughts are shaped by their native languages,and speakers of different languages think differently relevantly.The hypothesis is controversial partly because it seems to deny the possibility of a general principle for human cognition,and partly because some findings taken to support it have not reliably replicated.The author argued that considering this hypothesis through the lens of probabilistic inference has the potential to figure out both issues,at least with respect to certain prominent findings in the two languages—Chinese and English.After exploring on the inner relationship among language,thought and culture with the comparison between English and Chinese based on a series of examples including“numbers,Wuhan dialect and some different understandings of idioms”,the author made an inference that language can somewhat affect human thought under the different culture contexts.Besides,it also provides some reference for educators to take in-depth studies on the relationship among language,thought and culture,which is vitally significant for ESL educators and learners.展开更多
The researches on Critical Period Hypothesis(CPH) aims to explain the importance of the age factor in the process of learning a second language.In this essay,a critical review of the theoretical issues and empirical r...The researches on Critical Period Hypothesis(CPH) aims to explain the importance of the age factor in the process of learning a second language.In this essay,a critical review of the theoretical issues and empirical research on the CPH will spread out.Meanwhile,the discussion of implication and limitation of the CPH research will be concerned as well.展开更多
Krashen has developed the Input Hypothesis, which has deep influence on teaching method of second language. This thesis focuses on the Krashen's Input Hypothesis, which includes the following five hypotheses: the ...Krashen has developed the Input Hypothesis, which has deep influence on teaching method of second language. This thesis focuses on the Krashen's Input Hypothesis, which includes the following five hypotheses: the acquisition- learning hypothesis, the monitor hypothesis, the natural order hypothesis, the input hypothesis and the effective filter hypothesis. The thesis tries to explore the pedagogical implications of Krashen's Input Hypothesis on second language teaching in the aspects of the input quantity and input quality. The thesis tries to explore the most effective methods of second language teaching, in the hope that it will help to improve the efficiency of second language teaching.展开更多
AIM To propose a hypothesis defining theabsorption,distribution,metabolism andelimination of traditional Chinese recipe(TCR)-component in blood of healthy subjects andpatients,and estimate its correctness.METHODS Th...AIM To propose a hypothesis defining theabsorption,distribution,metabolism andelimination of traditional Chinese recipe(TCR)-component in blood of healthy subjects andpatients,and estimate its correctness.METHODS The pharmacokinetics(PK)of samedose of drug was studied in the animal model oftraditional Chinese syndrome(S)and healthyanimals.The classification,terminology,concept and significance of the hypothesis wereset forth with evidence provided in the presentstudy.The hypotheses consisted of traditionalChinese syndrome PK(S-PK)and traditionalChinese recipe PK(R-PK).Firstly,the observedtetramethylpyrazine(TMP)PK in healthy,chronically reserpinized rats(rat model ofspleen deficiency syndrome,RMSDS)andRMSDS treated with Sijunzi decoction(SJZD)forconfirmation were used to verify S-PK; secondly,the ferulic acid(FA)PK in healthy andhigh molecular weight dextran(HMWD)-inducedrabbit model with blood stasis syndrome(RDBSS)was also used to verify S-PK;andlastly,TMP PK parameters in serum of healthyrats after orally taken Ligusticum wallichii(LW),LW and Salvia miltiorrhiza(LW&SM)decoctions were compared to verify R-PK.RESULTS The apparent first-order absorption[Ka,(13.61±2.56)h<sup>-1</sup>,area under the blooddrug concentration-time curve[AUC,(24.88±9.76)μg.h<sup>-1</sup>mL<sup>-1</sup>],maximum drug concentration[C<sub>max</sub>,(4.82±1.23)μg·mL<sup>-1</sup>]of serum TMP inRMSDS were increased markedly(P【0.05)compared with those[Ka=(5.41±1.91)h<sup>-1</sup>,AUC=(5.20±2.57)μg·h<sup>-1</sup>·mL<sup>-1</sup>,C<sub>max</sub>=(2.33±1.77)μg·mL<sup>-1</sup>]of healthy rats(HR).Theapparent first-order rate constant for α and βdistribution phase[α=(0.38±0.09)h<sup>-1</sup>,β=(0.06±0.03)h<sup>-1</sup>,the apparent first-orderintercompartmental transfer rate constants[K<sub>10</sub>=(0.24±0.07)h<sup>-1</sup>,K<sub>12</sub>=(0.11±0.02)h<sup>-1</sup>,K<sub>21</sub>=(0.11±0.02)h<sup>-1</sup>]of serum TMP in RMSDS weredecreased significantly(P【0.01)comparedwith those[K<sub>10</sub>=(0.88±0.20)h<sup>-1</sup>,K<sub>12</sub>=(1.45±0.47)h<sup>-1</sup>,K<sub>21</sub>=(0.72±0.22)h<sup>-1</sup>]of HR.However,no apparent differences occurredbetween HR and RMSDS treated with SJZD.Theserum FA concentration and its AUC[(5.6690±2.3541)μg·h<sup>-1</sup>·mL<sup>-1</sup>] in RMBSS were also higherthan those[AUC=(2.7566±0.8232)μg·h<sup>-1</sup>·mL<sup>-1</sup>]of healthy rabbits(P【0.05).The Ka(11.51±2.82)h<sup>-1</sup>,AUC(0.84±0.17)μg·h<sup>-1</sup>·mL<sup>-1</sup>of LW & SM-derived TMP in serum weremuch lower(P【0.05)than those[Ka=(19.58±4.14)h<sup>-1</sup>,AUC=(1.27±0.26)μg·h<sup>-1</sup>·mL<sup>-1</sup>]ofLW-derived TMP in serum after oral decoctions.CONCLUSION The SDS and blood stasissyndrome state could affect significantly thepharmacokinetic parameters of drugs and theabnormal SDS pharmacokinetic parameters couldbe normalized by SJZD.The combination ofChinese medicine in TCR could reciprocallyaffect the pharmacokinetic parameters of othercomponents absorbed into the systemiccirculation.These results support the S-and R-PK hypothesis.展开更多
The hygiene hypothesis is thought to be a significant contributor to the growing incidence of inflammatory bowel disease (IBD) around the world, although the evidence for specific factors that underlie the hygiene hyp...The hygiene hypothesis is thought to be a significant contributor to the growing incidence of inflammatory bowel disease (IBD) around the world, although the evidence for specific factors that underlie the hygiene hypothesis in IBD is unclear. We aimed to systematically review the literature to determine which hygiene-related factors are associated with the development of IBD. Publications identified from a broad based MEDLINE and Current Contents search between 1966 and 2007 on key terms relevant to the 'hygiene hypothesis' and IBD including H pylori exposure, helminths, cold chain hypothesis, measles infection and vaccination, antibiotic use, breastfeeding, family size, sibship, urban upbringing, day care attendance and domestic hygiene were reviewed. The literature suggests that the hygiene hypothesis and its association with decreased microbial exposure in childhood probably plays an important role in the development of IBD, although the strength of the supporting data for each of the factors varies considerably. The most promising factors that may potentially be associated with development of IBD include H pylori exposure, helminths, breastfeeding and sibship. However, the vast majority of studies in this area are plagued by serious methodological shortcomings, particularly the reliance on retrospective recall of information making it difficult to truly ascertain the importance of a 'hygiene hypothesis' in IBD. The 'hygiene hypothesis' in IBD is an important area of research that may give clues to the aetiology of this disease. Directions for future research are recommended.展开更多
文摘In the scientific study of the faculty of language,M.Hauser,N.Chomsky & T.Fitch have proposed the recursion-only hypothesis in the context of biological evolution,while R.Jackendoff & S.Pinker have put forward a strong refutation---the language-as-adaptation hypothesis.This paper briefly introduces HCF hypothesis,meanwhile examines PJ's critical comment,and finally attempts to comment on both hypothesis with a balanced view.
文摘This paper indicates the problem of the famous Riemann hypothesis (RH), which has been well-verified by a definite answering method using a Bose-Einstein Condensate (BEC) phase. We adopt mathematical induction, mappings, and laser photons governed by electromagnetically induced transparency (EIT) to examine the existence of the RH. In considering the well-developed as Riemann zeta function, we find that the existence of RH has a corrected and self-consistent solution. Specifically, there is the only one pole at s = 1 on the complex plane for Riemann’s functions, which generalizes to all non-trivial zeros while s > 1. The essential solution is based on the BEC phases and on the nature of the laser photon(s). This work also incorporates Heisenberg commutators [ x^,p^]=1/2in the field of quantum mechanics. We found that a satisfactory solution for the RH would be incomplete without the formalism of Heisenberg commutators, BEC phases, and EIT effects. Ultimately, we propose the application of qubits in connection with the RH.
文摘The Porter Hypothesis,proposed by Michael E.Porter,suggests that stringent environmental regulations can enhance corporate innovation and competitiveness,challenging the traditional view that regulations increase business costs.It argues that regulations motivate firms to innovate,leading to improved productivity,cost reductions,and new market opportunities.However,there are proponents and critics in academia regarding the hypothesis.Supporters claim regulations change corporate behavior,reducing agency costs and boosting research and development.Critics argue that if win-win situations exist,businesses would naturally pursue them without regulatory incentives.Key challenges in proving or refuting the hypothesis include its various versions,the difficulty in quantifying innovation and competitiveness,the complex interplay between regulation,innovation,and competitiveness,and the varying impacts across industries and regions.Additionally,the effects may require a long time to manifest,and the hypothesis’s applicability is influenced by evolving environmental policies and market environments.Despite mixed empirical findings,the Porter Hypothesis provides a valuable framework for understanding the relationships among environmental regulation,innovation,and competitiveness,but its validation requires a more comprehensive assessment.
基金国家自然科学基金面上项目“基于高压人群身心健康的工作环境绿色空间体系研究”(编号51978364)国家自然科学基金青年科学基金项目“北京地区城市森林疗养空间特征识别及健康效益定量评价”(编号51908310)Tsinghua-Toyota Joint Research Institute Cross discipline Program共同资助。
基金supported by grants to DD from Agencia Nacional de Promoción de la Investigación,el desarrollo tecnológico y la innovación(ANPCyT,PICT N°03893).
文摘In light of the rising evidence of the association between viral and bacterial infections and neurodegeneration,we aimed at revisiting the infectious hypothesis of Alzheimer’s disease and analyzing the possible implications of COVID-19 neurological sequelae in long-term neurodegeneration.We wondered how SARS-CoV-2 could be related to the amyloid-βcascade and how it could lead to the pathological hallmarks of the disease.We also predict a paradigm change in clinical medicine,which now has a great opportunity to conduct prospective surveillance of cognitive sequelae and progression to dementia in people who suffered severe infections together with other risk factors for Alzheimer’s disease.
文摘Soil liquefaction is one of the complex research topics in geotechnical engineering and engineering geology. Especially after the 1964 Niigata earthquake (Japan) induced many soil liquefaction incidents, a variety of soil liquefaction studies were conducted and reported, including the liquefaction potential assessment methods utilizing the shear wave velocity (V<sub>s</sub>) or SPT-N profiles (SPT: standard penetration test). This study used the V<sub>s</sub> and SPT methods recommended by the National Center for Earthquake Engineering Research (NCEER) to examine which is more conservative according to the assessment results on 41 liquefiable soil layers at sites in two major cities in Taiwan. Statistical hypothesis testing was used to make the analysis more quantitative and objective. Based on three sets of hypothesis tests, it shows that the hypothesis—the SPT method is more conservative than the V<sub>s</sub> method—was not rejected on a 5% level of significance.
文摘Aiming at gradually developing and perfecting the task-based teaching method, the essay, with enlightment from the Krashen's Input Hypothesis, discusses some issues about input, output, activities and teacher's role in this method.
文摘Aim To study the rules governing pressure distribution of traveling charge under the condition of Lagrange hypothesis. Methods\ The study is based on the laws of conservation of momentum and energy. Results\ The gas flow velocity distribution formula at the back of a projectile and the momentum equation of a traveling charge are deduced, and rules governing their pressure distribution under the Lagrange hypothesis conditions are established. The pressure distribution of a traveling charge is compared with that of a conventional charge. Conclusion\ The pressure distribution in the bore of a traveling charge can be accurately predicted. A parabolic pressure distribution type is revealed.
文摘Sapir-Whorf hypothesis has its implication in translation studies. Each language is a peculiar whole. It is a product, even an expression, of the spiritual personality and the cultural particularity. Translation is a kind of interlingual and intercultural communication. It involves not only the transference from one language into another, but a whole set of extra-linguistic criteria. In translating we are always crossing a greater or lesser barrier or divide.
文摘“Sapir-Whorf hypothesis"holds that human thoughts are shaped by their native languages,and speakers of different languages think differently relevantly.The hypothesis is controversial partly because it seems to deny the possibility of a general principle for human cognition,and partly because some findings taken to support it have not reliably replicated.The author argued that considering this hypothesis through the lens of probabilistic inference has the potential to figure out both issues,at least with respect to certain prominent findings in the two languages—Chinese and English.After exploring on the inner relationship among language,thought and culture with the comparison between English and Chinese based on a series of examples including“numbers,Wuhan dialect and some different understandings of idioms”,the author made an inference that language can somewhat affect human thought under the different culture contexts.Besides,it also provides some reference for educators to take in-depth studies on the relationship among language,thought and culture,which is vitally significant for ESL educators and learners.
文摘The researches on Critical Period Hypothesis(CPH) aims to explain the importance of the age factor in the process of learning a second language.In this essay,a critical review of the theoretical issues and empirical research on the CPH will spread out.Meanwhile,the discussion of implication and limitation of the CPH research will be concerned as well.
文摘Krashen has developed the Input Hypothesis, which has deep influence on teaching method of second language. This thesis focuses on the Krashen's Input Hypothesis, which includes the following five hypotheses: the acquisition- learning hypothesis, the monitor hypothesis, the natural order hypothesis, the input hypothesis and the effective filter hypothesis. The thesis tries to explore the pedagogical implications of Krashen's Input Hypothesis on second language teaching in the aspects of the input quantity and input quality. The thesis tries to explore the most effective methods of second language teaching, in the hope that it will help to improve the efficiency of second language teaching.
基金National Natural Science Foundation of China,No.398709323967086539570870 and 39100139.
文摘AIM To propose a hypothesis defining theabsorption,distribution,metabolism andelimination of traditional Chinese recipe(TCR)-component in blood of healthy subjects andpatients,and estimate its correctness.METHODS The pharmacokinetics(PK)of samedose of drug was studied in the animal model oftraditional Chinese syndrome(S)and healthyanimals.The classification,terminology,concept and significance of the hypothesis wereset forth with evidence provided in the presentstudy.The hypotheses consisted of traditionalChinese syndrome PK(S-PK)and traditionalChinese recipe PK(R-PK).Firstly,the observedtetramethylpyrazine(TMP)PK in healthy,chronically reserpinized rats(rat model ofspleen deficiency syndrome,RMSDS)andRMSDS treated with Sijunzi decoction(SJZD)forconfirmation were used to verify S-PK; secondly,the ferulic acid(FA)PK in healthy andhigh molecular weight dextran(HMWD)-inducedrabbit model with blood stasis syndrome(RDBSS)was also used to verify S-PK;andlastly,TMP PK parameters in serum of healthyrats after orally taken Ligusticum wallichii(LW),LW and Salvia miltiorrhiza(LW&SM)decoctions were compared to verify R-PK.RESULTS The apparent first-order absorption[Ka,(13.61±2.56)h<sup>-1</sup>,area under the blooddrug concentration-time curve[AUC,(24.88±9.76)μg.h<sup>-1</sup>mL<sup>-1</sup>],maximum drug concentration[C<sub>max</sub>,(4.82±1.23)μg·mL<sup>-1</sup>]of serum TMP inRMSDS were increased markedly(P【0.05)compared with those[Ka=(5.41±1.91)h<sup>-1</sup>,AUC=(5.20±2.57)μg·h<sup>-1</sup>·mL<sup>-1</sup>,C<sub>max</sub>=(2.33±1.77)μg·mL<sup>-1</sup>]of healthy rats(HR).Theapparent first-order rate constant for α and βdistribution phase[α=(0.38±0.09)h<sup>-1</sup>,β=(0.06±0.03)h<sup>-1</sup>,the apparent first-orderintercompartmental transfer rate constants[K<sub>10</sub>=(0.24±0.07)h<sup>-1</sup>,K<sub>12</sub>=(0.11±0.02)h<sup>-1</sup>,K<sub>21</sub>=(0.11±0.02)h<sup>-1</sup>]of serum TMP in RMSDS weredecreased significantly(P【0.01)comparedwith those[K<sub>10</sub>=(0.88±0.20)h<sup>-1</sup>,K<sub>12</sub>=(1.45±0.47)h<sup>-1</sup>,K<sub>21</sub>=(0.72±0.22)h<sup>-1</sup>]of HR.However,no apparent differences occurredbetween HR and RMSDS treated with SJZD.Theserum FA concentration and its AUC[(5.6690±2.3541)μg·h<sup>-1</sup>·mL<sup>-1</sup>] in RMBSS were also higherthan those[AUC=(2.7566±0.8232)μg·h<sup>-1</sup>·mL<sup>-1</sup>]of healthy rabbits(P【0.05).The Ka(11.51±2.82)h<sup>-1</sup>,AUC(0.84±0.17)μg·h<sup>-1</sup>·mL<sup>-1</sup>of LW & SM-derived TMP in serum weremuch lower(P【0.05)than those[Ka=(19.58±4.14)h<sup>-1</sup>,AUC=(1.27±0.26)μg·h<sup>-1</sup>·mL<sup>-1</sup>]ofLW-derived TMP in serum after oral decoctions.CONCLUSION The SDS and blood stasissyndrome state could affect significantly thepharmacokinetic parameters of drugs and theabnormal SDS pharmacokinetic parameters couldbe normalized by SJZD.The combination ofChinese medicine in TCR could reciprocallyaffect the pharmacokinetic parameters of othercomponents absorbed into the systemiccirculation.These results support the S-and R-PK hypothesis.
文摘The hygiene hypothesis is thought to be a significant contributor to the growing incidence of inflammatory bowel disease (IBD) around the world, although the evidence for specific factors that underlie the hygiene hypothesis in IBD is unclear. We aimed to systematically review the literature to determine which hygiene-related factors are associated with the development of IBD. Publications identified from a broad based MEDLINE and Current Contents search between 1966 and 2007 on key terms relevant to the 'hygiene hypothesis' and IBD including H pylori exposure, helminths, cold chain hypothesis, measles infection and vaccination, antibiotic use, breastfeeding, family size, sibship, urban upbringing, day care attendance and domestic hygiene were reviewed. The literature suggests that the hygiene hypothesis and its association with decreased microbial exposure in childhood probably plays an important role in the development of IBD, although the strength of the supporting data for each of the factors varies considerably. The most promising factors that may potentially be associated with development of IBD include H pylori exposure, helminths, breastfeeding and sibship. However, the vast majority of studies in this area are plagued by serious methodological shortcomings, particularly the reliance on retrospective recall of information making it difficult to truly ascertain the importance of a 'hygiene hypothesis' in IBD. The 'hygiene hypothesis' in IBD is an important area of research that may give clues to the aetiology of this disease. Directions for future research are recommended.