This article has Open Peer Review reports available.
Exploration of risk taking behaviors and perceived susceptibility of colorectal cancer among Malaysian adults: a community based cross-sectional study
© Al-Dubai et al.; licensee BioMed Central Ltd. 2013
Received: 28 March 2013
Accepted: 2 October 2013
Published: 7 October 2013
Perceived susceptibility to an illness has been shown to affect Health-risk behavior. The objective of the present study was to determine the risk taking behaviors and the demographic predictors of perceived susceptibility to colorectal cancer in a population-based sample.
A cross-sectional study was carried out among 305 Malaysian adults in six major districts, selected from urban, semi-urban, and rural settings in one state in Malaysia. A self-administered questionnaire was used in this study. It was comprised of socio-demographics, risk-taking behaviors, and validated domains of the Health Belief Model (HBM).
The mean (± SD) age of the respondents was 34.5 (± 9.6) and the majority (59.0%) of them were 30 years or older. Almost 20.7% of the respondents felt they were susceptible to colorectal cancer. Self-reported perceived susceptibility mirrored unsatisfactory screening behaviors owing to the lack of doctors’ recommendation, ignorance of screening modalities, procrastination, and the perception that screening was unnecessary. Factors significantly associated with perceived susceptibility to colorectal cancer were gender (OR = 1.8, 95% CI 1.0-3.3), age (OR = 2. 2, 95% CI 1.2-4.0), ethnicity (OR = 0. 3, 95% CI 0.2-0.6), family history of colorectal cancer (OR = 3. 2, 95% CI 1.4-7.4) and alcohol intake (OR = 3.9, 95% CI 2.1-7.5).
The present study revealed that screening behavior among respondents was unsatisfactory. Hence, awareness of the importance of screening to prevent colorectal cancers is imperative.
Colorectal cancer (CRC) is one of the most common malignancies among adults in both developed and developing countries . Currently, it is the third most commonly diagnosed malignancy and the fourth leading cause of death worldwide , with more than 940,000 cases diagnosed annually . Recent reports indicate that it is the fastest emerging gastrointestinal tract cancer in Asia Pacific . In Malaysia, CRC is the most common malignancy in men and the third commonest malignancy in women (after breast and cervical cancer) .
Colorectal cancer is characterized as developing over long periods of time and is a localized and curable condition . The survival rate for localized disease is 90%, compared to less than 10% for metastatic disease . Screening for CRC has been shown to reduce mortality as it facilitates early detection and prevention of the malignancy [8–10]. The recommended screening methods for early detection of colorectal cancer are fecal occult blood test (FOBT), flexible sigmoidoscopy , barium enema and colonoscopy .
Risk taking behaviors are associated with perceived susceptibility for cancer . Individuals engaged in detrimental health behaviors would perceive a higher susceptibility to malignancies . Smokers were found to perceive a higher susceptibility of developing cancer than non-smokers [15, 16]. In a meta-analysis study, a significant association was found between perceived a susceptibility of colorectal cancer and the consumption of fruits and vegetable . Alcohol consumption, obesity and low levels of activity were also reported as risk factors of CRC [18–20].
Social cognitive frameworks in preventive health, namely the Health Belief Model (HBM) , the Protection Motivation Theory , and the Precaution Adoption Process Model  view risk perceptions with perceived susceptibility as a catalyst for primary prevention . Perceived susceptibility advocates the “motivational engine” for precautionary behaviors . However, social cognitive critics debate the validity of variables from these models, which tend to predict behavioral intention rather than the behavior itself . McQueen et al., (2010) posed the alternate hypothesis that perceived susceptibility advocates change in psychosocial predictors influencing subsequent intentions and behavior . The HBM relates a socio-psychological theory of decision making to the individual health-related behaviors and it included four dimensions: Susceptibility, Severity, Benefits and Costs . This study believes that understanding the determinants of perceived susceptibility to colorectal cancer is a crucial element in constructing cancer preventive health behaviors.
This study aims to explore risk taking behaviors and perceived susceptibility to colorectal cancer among healthy communities from different geographical settings (urban, semi-urban and rural) and ages. This study will overcome gaps and weaknesses of previous studies by expanding its socio-demographic factors and other relevant covariates concerning colorectal cancer susceptibility and screening behaviors by using the validated Health Belief Model (HBM)  among the Malaysian population.
Study setting and population
A community-based cross-sectional study was conducted in three different geographical settings (urban, semi-urban, and rural areas) within the state of Selangor, Malaysia. This state includes six major districts, namely Subang Jaya, Petaling Jaya, Selayang, Klang, Kuala Selangor and Kuala Langat. Subang Jaya and Petaling Jaya are urban settings, Selayang and Klang are semi-urban, and Kuala Selangor and Kuala Langat are rural. The sample size required for this study was estimated to be 280 respondents. This calculation was based on previous study parameters  using Lwanga and Lemeshow’s equation (1991). We added 10% of the calculated sample size (28) to compensate for missing data or non-response and so the sample size rose to 308. Respondents aged ≥18 years, and who lived for at least one year in these districts, were also included in this study. Respondents were approached at various commercial settings and major streets within the selected residential areas using convenience sampling. Questionnaires were administered in both English and the local language.
The purpose of the study was explained to respondents. Confidentiality and their right to withdraw were ensured. Participants received a written description of the purpose and aims of the study along with the study questionnaires and participant consent was obtained. Approval was obtained from the ethics committee of the International Medical School in the Management and Science University (MSU), Malaysia.
A self-administered questionnaire was developed using previous literatures and the validated Health Belief Model Scale (HBM) for colorectal cancer . Socio-demographics included 10 questions relating to gender, age, race, residency area, marital status, level of education, occupation, family income, family history of any cancer, and family history of colorectal cancer. We designed a five-item mini-subscale to assess the risk taking behaviors of colorectal cancer (smoking, alcohol intake, fruits and vegetable consumption, exercise and obesity). The Body Mass Index (BMI) was calculated as weight in kilograms divided by height in square meters (kg/m2). This study adopted the World Health Organisation’s (WHO) BMI cut-off points for Asian populations. A BMI <18.5 kg/m2 was categorized as underweight, 18 · 5–22 · 9 kg/m2 as normal and ≥ 23.0 kg/m2 as overweight. The latter was further classified as pre-obese (23.0–27.4 kg/m2), obese Class I (27.5–34.9 kg/m2), obese Class II (35.0–39.9 kg/m2), and obese Class III (≥ 40 kg/m2) . To ease analysis “underweight” and “normal range” were categorized as 'normal’ while “pre-obese” and “obese Class I, II and III” were categorized as 'obese’. The validated HBM was used in this study. It assessed four main constructs namely: perceived susceptibility (1 item), perceived severity (1 item), perceived benefits (1 item) and perceived barriers (17 items) . Response options include “Agree” or “Disagree”. the questionnaire was pilot-tested among 10 respondents.
Data analysis was performed using the Statistical Package of Social Sciences (SPSS) software, version 16.0. Descriptive statistics were obtained for all variables in the study. The chi-square test was used to assess the association between perceived susceptibility and categorical variables in this study. For variables with three or more categories, simple logistic regression analysis was used to obtain the odds ratio (OR). Multiple logistic regression analysis using the Backward Wald technique was performed to obtain factors associated with perceived susceptibility to colorectal cancer. All independent variables that had significant associations with perceived susceptibility in bivariate analysis were included in the multivariate analysis. Multi-collinearity between independent variables was checked for by the values of standard errors (SE). The accepted level of significance in this study was set below 0.05 (p < 0.05).
Socio-demographic characteristics of the respondents
Socio -demographic characteristics of respondents (n = 305)
≤ 30 years
> 30 years
High school or less
Family income (MYR) /month*
Family history of any cancer
Family history of colorectal cancer
Risk taking behaviors of colorectal cancer among respondents
Risk taking behaviors of colorectal cancer among respondents (n = 305)
< 3 times per week
≥ 3 times per week
Consuming fruits & vegetable
< 3 times per week
≥ 3 times per week
Perception of colorectal cancer and screening according to Health Belief Model
Perception of colorectal cancer and screening among respondents (n = 305)
My chance of getting colorectal cancer is great
Colorectal cancer may be serious if it is found late
If I have colorectal cancer, I will have a good chance of survival if the cancer is found early
Reasons for not getting FOBT
Didn’t know I should have it
Do not think it’s necessary
Not recommended by my doctor
I don’t have health problems
Concerns about FOBT
Worried that FOBT is messy
Worried that FOBT is inconvenient
Reasons for not getting FlexibleSigmoidoscopy
I don’t know I should have it
I don’t think it’s necessary
It was not recommended by my doctor
I have no symptoms
It is painful
Concerns about Flexible Sigmoidoscopy
Worried that Flexible Sigmoidoscopy is embarrassing
Worried that Flexible Sigmoidoscopy is painful
Perceived barriers to CRC screening
Fear of discovering cancer
Perceived susceptibility to colorectal cancer by socio-demographic characteristics
Association between perceived susceptibility of colorectal cancer and demographic variables (n = 305)
Perceived higher chance of having colorectal cancer
Perceived lower chance of having colorectal cancer
≤ 30 years
> 30 years
High school or less
Family income (MYR)*
Family history of any cancer
Family history of colorectal cancer
Association between risk taking behaviors and perceived susceptibility to colorectal cancer
Association between risk taking behaviors and perceived susceptibility among respondents (n = 305)
Believe chance of having colorectal cancer is high
Less than three times per week
Three or more times per week
Consume fruits and vegetable
Less than three times per week
Three or more times per week
Body Mass Index (BMI)
Factors associated with perceived susceptibility among respondents in multiple logistic regression analysis
Multiple logistic regression analysis (Backward Wald); predictors of perceived susceptibility among respondents (n = 305)
≤ 30 years
> 30 years
This study aimed to explore risk taking behaviors and determine potential factors affecting perceived susceptibility to colorectal cancer among the Malaysian population. Of the 305 respondents surveyed, 20.7% perceived high chances of having colorectal cancer. In the final model, age and race were significantly associated with perceived susceptibility to colorectal cancer.
To the best of our knowledge, this study was the first Malaysian study to assess self-reported risk-taking behaviour and perceived susceptibility to colorectal cancer. The estimated rate of perceived susceptibility reported in the present study was comparatively higher to that found in a British sample (17%)  but relatively lower than that reported from the United States of America (USA)(29-50%) [29–31].
Health behavioral theories predicted higher intentions of preventive actions among individuals with greater susceptibility to a disease [13, 32]. However, in the present study, self-reported susceptibility mirrored unsatisfactory preventive behaviours. The barriers to screening for colorectal cancer in this study were consistent with previous studies from Malaysia on the barriers of CRC screening  and USA [8, 34].
In the present study, perceived susceptibility to colorectal cancer was significantly higher among men. A previous study by Wardle et al., (2005)  found that men had low perceived susceptibility while some studies found no relationship between gender and perceived susceptibility [36–38]. Our study’s findings on the association between perceived susceptibility and age was consistent with previous studies [14, 39].
A new finding in this study was the significant association between perceived susceptibility and race. Despite the high incidence of colorectal cancer among ethnic Chinese in Malaysia , this study found higher perceived susceptibility among ethnic Malays and Indians in comparison to Chinese. A possible explanation could be due to a lack of information among respondents. In the literature, the association between ethnicity and perceived susceptibility was masked. A study by Shokar et al., (1990) concluded that whites were more likely to contract colorectal cancer than blacks.
This study also found a significant association between alcohol intake and the perceived susceptibility to colorectal cancer which was, again, consistent with a previous study . Our finding of the relationship between smoking and perceived susceptibility was inconsistent with some previous studies [15, 16]. Although some longitudinal studies had observed a positive relationship between perceived risk and subsequent behaviour, that association was weak and unsatisfactory. Some studies, however, find no association or even a negative one [32, 42].
The cross-sectional design of the current study can test the “accuracy hypothesis” that asserts that perceptions of risk at a certain time properly reflect one’s risk behaviours at that time . Thus, this design can be useful for identifying information deficits and the areas where further education is needed. The failure of the current study to find an association between the perceived susceptibility and risk taking behaviors could be attributed to the natural causal relationship between those variables in which the cross-sectional design was not appropriate . A second possible reason could be due to an inadequate specification of the links between perceived susceptibility and risk taking behaviour in the study questionnaire. In other words, our respondents may not answer the “perceived susceptibility” questions according to their awareness that smoking is a risk for developing cancer. To avoid such bias in the future, this study recommends phrasing the question in another way, for example, “If you don’t change your smoking behaviour, what is your chance of getting colorectal cancer in the future?” By using such a question, we can link the perceived susceptibility to the behaviour. An alternative way is to assess the relationship between the perceived susceptibility and the intention to quit or stop the risky behaviours. Although intentions may not necessarily predict or reflect the actual behaviours, it could be considered as an intermediate step towards action.
The cross-sectional nature of this study could not establish the causal relationships between perceived susceptibility and behaviour. Thus, further exploration is required through prospective and meta-analysis studies.
This study found unsatisfactory screening behaviors due to the lack of doctors’ recommendation, unawareness of screening modalities, procrastination, and a negative apprehension that screening was unnecessary. Perceived susceptibility was associated significantly with age, race, and alcohol intake. Community health education and a health promotion program of colorectal cancer risk factors and screening methods should be conducted among the community. Doctors and health care providers should be engaged in public education.
- Jemal A, Bray F, Center MM, Ferlay J, Ward E, Forman D: Global cancer statistics. CA Cancer J Clin. 2011, 61 (2): 69-90. 10.3322/caac.20107.View ArticlePubMedGoogle Scholar
- Salimzadeh H, Delavari A, Montazeri A, Mirzazadeh A: Knowledge and practice of Iranians towards colorectal cancer, and barriers to screening. Int J Prev Med. 2012, 3: 29-35.PubMedPubMed CentralGoogle Scholar
- Siegel R, Ward E, Brawley O, Jemal A: Cancer statistics, 2011. CA Cancer J Clin. 2011, 61 (4): 212-236. 10.3322/caac.20121.View ArticlePubMedGoogle Scholar
- Sung JJ, Choi SY, Chan FK, Ching JY, Lau JT, Griffiths S: Obstacles to colorectal cancer screening in Chinese: a study based on the health belief model. Am J Gastroenterol. 2005, 103: 974-981.View ArticleGoogle Scholar
- Lim GCC, Rampal S, Halimah Y: National Cancer Registry Kuala Lumpur. Cancer Incidence in Peninsular Malaysia 2003-2005. 2008, http://www.moh.gov.my/images/gallery/Report/Cancer/CancerIncidenceinPeninsularMalaysia2003-2005x1x.pdf,Google Scholar
- Young G, Rozen P, Levin B: How does colorectal cancer develop? Colorectal cancer in clinical practice: prevention, early detection and management. Abingdon: Taylor and Francis. 2006, 2: 27-46.Google Scholar
- Jemal A, Siegel R, Ward E, Hao Y, Xu J, Murray T, Thun MJ: Cancer statistics. CA Cancer J Clin. 2008, 58 (2): 71-96. 10.3322/CA.2007.0010.View ArticlePubMedGoogle Scholar
- Dolan NC, Ferreira MR, Davis TC, Fitzgibbon ML, Rademaker A, Liu D, Schmitt BP, Gorby N, Wolf M, Bennett CL: Colorectal cancer screening knowledge, attitudes, and beliefs among veterans: does literacy make a difference?. JCO. 2004, 22 (13): 2617-2622. 10.1200/JCO.2004.10.149.View ArticleGoogle Scholar
- Steele RJ, McClements PL, Libby G, Black R, Morton C, Birrel J, Mowat NAG: Results from the first three rounds of the Scottish demonstration pilot of FOBT screening for colorectal cancer. Gut. 2009, 58: 530-535. 10.1136/gut.2008.162883.View ArticlePubMedGoogle Scholar
- Atkin WS, Edwards R, Kralj-Hans I, Wooldrage K, Hart AR, Northover J, Parkin DM, Wardle J, Duffy SW, Cuzick J: Once-only flexible sigmoidoscopy screening in prevention of colorectal cancer: a multicentre randomised controlled trial. Lancet. 2010, 375 (9726): 1624-1633. 10.1016/S0140-6736(10)60551-X.View ArticlePubMedGoogle Scholar
- Zauber AG, Winawer SJ, O’Brien MJ, Lansdorp-Vogelaar I, van Ballegooijen M, Hankey BF, Shi W, Bond JH, Schapiro M, Panish JF: Colonoscopic polypectomy and long-term prevention of colorectal-cancer deaths. N Engl J Med. 2012, 366 (8): 687-696. 10.1056/NEJMoa1100370.View ArticlePubMedPubMed CentralGoogle Scholar
- Ford JS, Coups EJ, Hay JL: Knowledge of colon cancer screening in a national probability sample in the United States. J Health Commun. 2006, 11: 19-35. 10.1080/10810730600637533.View ArticlePubMedGoogle Scholar
- Robb KA, Miles A, Wardle J: Perceived risk of colorectal cancer: sources of risk judgements. Cancer Epidemiol Biomarkers Prev. 2007, 16: 694-702. 10.1158/1055-9965.EPI-06-0151.View ArticlePubMedGoogle Scholar
- Robb KA, Miles A, Wardle J: Demographic and psychosocial factors associated with perceived risk for colorectal cancer. Cancer Epidemiol Biomarkers Prev. 2004, 13: 366-372.PubMedGoogle Scholar
- Bleiker E, Menko FH, Taal BG, Kluijt I, Wever LD, Gerritsma MA, Vasen HF, Aaronson NK: Screening behavior of individuals at high risk for colorectal cancer. Gastroenterology. 2005, 128 (2): 280-287. 10.1053/j.gastro.2004.11.002.View ArticlePubMedGoogle Scholar
- Green AR, Betancourt JR, Richter JM, Janairo M-PR, Gamba GB, Atlas SJ: Barriers to screening colonoscopy for low-income Latino and white patients in an urban community health center. J Gen Intern Med. 2008, 23 (6): 834-840. 10.1007/s11606-008-0572-6.View ArticlePubMedPubMed CentralGoogle Scholar
- Aune D, Chan DS, Lau R, Vieira R, Greenwood DC, Kampman E, Norat T: Dietary fibre, whole grains, and risk of colorectal cancer: systematic review and dose-response meta-analysis of prospective studies. BMJ. 2011, 343: d6617-10.1136/bmj.d6617.View ArticlePubMedPubMed CentralGoogle Scholar
- Huxley HA, Clifton P, Czernichow S, Parr CL, Woodward M: The impact of dietary and lifestyle risk factors on risk of colorectal cancer: A quantitative overview of the epidemiological evidence. Int J Cancer. 2009, 125: 171-180. 10.1002/ijc.24343.View ArticlePubMedGoogle Scholar
- Pelucchi C, Tramacere I, Boffetta P, Negri E, La Vecchia C: Alcohol consumption and cancer risk. Nutr Cancer. 2011, 63: 983-990. 10.1080/01635581.2011.596642.View ArticlePubMedGoogle Scholar
- Parkin DM, Boyd L, Walker LC: The fraction of cancer attributable to lifestyle and environmental factors in the UK in 2010. Br J Cancer. 2011, 105 (Suppl 2): 77-81.View ArticleGoogle Scholar
- Rosenstock IM: Historical origins of the health belief model. Health Educ Monogr. 1974, 2: 1-8.Google Scholar
- Rogers RW: A protection motivation theory of fear appeals and attitude change. J Psychol. 1975, 91: 93-114. 10.1080/00223980.1975.9915803.View ArticleGoogle Scholar
- Weinstein ND: The precaution adoption process. Health Psychol. 1988, 7: 355-386.View ArticlePubMedGoogle Scholar
- Gregory TA, Wilson C, Duncan A, Turnbull D, Cole SR, Young G: Demographic, social cognitive and social ecological predictors of intention and participation in screening for colorectal cancer. BMC Public Health. 2011, 11: 38-10.1186/1471-2458-11-38. doi:10.1186/1471-2458-11-38View ArticlePubMedPubMed CentralGoogle Scholar
- Armitage CJ, Conner M: Social cognitive models and health behaviour: a structured review. Psychol and Health. 2000, 15: 173-189. 10.1080/08870440008400299.View ArticleGoogle Scholar
- McQueen A, Vernon SW, Rothman AJ, Norman GJ, Myers RE, Tilley BC: Examining the role of perceived susceptibility on colorectal cancer screening intention and behavior. Ann Behav Med. 2010, 40: 205-217. 10.1007/s12160-010-9215-3. doi:10.1007/s12160-010-9215-3View ArticlePubMedPubMed CentralGoogle Scholar
- Lwanga SK, Lemeshow S: Sample Size Determination in Health Studies: A Practical Manual. 1991, Geneva: World Health OrganizationGoogle Scholar
- WHO Expert Consultation: Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies. Lancet. 2004, 363: 157-163.View ArticleGoogle Scholar
- Shokar NK, Carlson CA, Weller SC: Factors associated with racial/ethnic differences in colorectal cancer screening. Am Board Family Med. 2008, 21 (5): 414-426. 10.3122/jabfm.2008.05.070266.View ArticleGoogle Scholar
- Lipkus IM, Rimer BK, Lyna PR, Pradhan AA, Conaway M, Woods-Powell CT: Colorectal screening patterns and perceptions of risk among African-American users of a community health center. J Commun Health. 1996, 21: 409-427. 10.1007/BF01702602.View ArticleGoogle Scholar
- Aiken LS, Fenaughty AM, West SG, Johnson JJ, Luckett TL: Perceived determinants of risk for breast cancer and the relations among objective risk, perceived risk, and screening behavior over time. Women Health. 1995, 1: 27-50.Google Scholar
- Vollrath M, Knoch D, Cassano L: Personality, risky health behaviour and perceived susceptibility to health risks. Eur J Pers. 1999, 13: 39-50. 10.1002/(SICI)1099-0984(199901/02)13:1<39::AID-PER328>3.0.CO;2-J.View ArticleGoogle Scholar
- Hilmi I, Hartono JL, Goh K: Negative perception in those at highest risk–potential challenges in colorectal cancer screening in an urban Asian population. Asian Pac J Cancer Prev. 2010, 11: 815-822.PubMedGoogle Scholar
- Rawl SM, Menon U, Champion VL, May FE, Loehrer P, Hunter C, Azzouz F, Monahan PO, Skinner CS: Do benefits and barriers differ by stage of adoption for colorectal cancer screening?. Health Educ Res. 2005, 20 (2): 137-148. doi:10.1093/her/cyg110View ArticlePubMedGoogle Scholar
- Wardle J, Miles A, Atkin W: Gender differences in utilization of colorectal cancer screening. Med Screen. 2005, 12: 20-27. 10.1258/0969141053279158.View ArticleGoogle Scholar
- Courtenay WH, McCreary DR, Merighi JR: Gender and ethnic differences in health beliefs and behaviours. J Health Psychol. 2002, 7: 219-231. 10.1177/1359105302007003216.View ArticlePubMedGoogle Scholar
- Lipkus IM, Klein WMP: Effects of communicating social comparison information on risk perceptions for colorectal cancer. J Health Commun. 2006, 11: 391-407. 10.1080/10810730600671870.View ArticlePubMedGoogle Scholar
- Domanska K, Nilbert M, Soller M, Silfverberg B, Carlsson C: Discrepancies between estimated and perceived risk of cancer among individuals with hereditary nonpolyposis colorectal cancer. Genet Test. 2007, 11 (2): 183-186. 10.1089/gte.2007.9999.View ArticlePubMedGoogle Scholar
- Codori AM, Waldeck T, Petersen GM, Miglioretti D, Trimbath JD, Tillery MA: Genetic counseling outcomes: perceived risk and distress after counseling for hereditary colorectal cancer. J Genet Couns. 2005, 14 (2): 119-132. 10.1007/s10897-005-4062-2.View ArticlePubMedGoogle Scholar
- Tilburt JC, James KM, Sinicrope PS, Eton DT, Costello BA, Carey J, Lane MA, Ehlers SL, Erwin PJ, Nowakowski KE, Murad MH: Factors influencing cancer risk perception in high risk population: a systemic review. Hereditary Cancer in Clin Pract. 2011, 9: 2-10.1186/1897-4287-9-2. doi:10.1186/1897-4287-9-2View ArticleGoogle Scholar
- Fedirko V, Tramacere I, Bagnardi V, Rota M, Scotti L, Islami F, Negri E, Straif K, Romieu I, La Vecchia C: Alcohol drinking and colorectal cancer risk: an overall and dose–response meta-analysis of published studies. Ann Oncol. 2011, 22 (9): 1958-1972. 10.1093/annonc/mdq653.View ArticlePubMedGoogle Scholar
- Brewer NT, Weinstein ND, Cuite CL, Herrington JE: Risk perceptions and their relation to risk behavior. Ann Behav Med. 2004, 27 (2): 125-130. 10.1207/s15324796abm2702_7.View ArticlePubMedGoogle Scholar
- The pre-publication history for this paper can be accessed here:http://www.biomedcentral.com/1471-2458/13/930/prepub
This article is published under license to BioMed Central Ltd. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.