The Protective Action Decision Model: Theoretical Modifications and Additional Evidence
Corresponding Author
Michael K. Lindell
Texas A&M University, Hazard Reduction & Recovery Center, College Station, TX, USA.
Michael K. Lindell, Texas A&M University, Hazard Reduction & Recovery Center, College Station, TX 77843-3137, USA; mlindell@tamu.eduSearch for more papers by this authorRonald W. Perry
Arizona State University, School of Public Affairs, Phoenix AZ, USA.
Search for more papers by this authorCorresponding Author
Michael K. Lindell
Texas A&M University, Hazard Reduction & Recovery Center, College Station, TX, USA.
Michael K. Lindell, Texas A&M University, Hazard Reduction & Recovery Center, College Station, TX 77843-3137, USA; mlindell@tamu.eduSearch for more papers by this authorRonald W. Perry
Arizona State University, School of Public Affairs, Phoenix AZ, USA.
Search for more papers by this authorAbstract
The Protective Action Decision Model (PADM) is a multistage model that is based on findings from research on people's responses to environmental hazards and disasters. The PADM integrates the processing of information derived from social and environmental cues with messages that social sources transmit through communication channels to those at risk. The PADM identifies three critical predecision processes (reception, attention, and comprehension of warnings or exposure, attention, and interpretation of environmental/social cues)—that precede all further processing. The revised model identifies three core perceptions—threat perceptions, protective action perceptions, and stakeholder perceptions—that form the basis for decisions about how to respond to an imminent or long-term threat. The outcome of the protective action decision-making process, together with situational facilitators and impediments, produces a behavioral response. In addition to describing the revised model and the research on which it is based, this article describes three applications (development of risk communication programs, evacuation modeling, and adoption of long-term hazard adjustments) and identifies some of the research needed to address unresolved issues.
References
- 1 Barton A. Communities in Disaster. New York : Doubleday, 1969.
- 2 Drabek TE. Human System Responses to Disaster: An Inventory of Sociological Findings. New York : Springer-Verlag, 1986.
- 3 Fritz CE. Disaster. In RK Merton, RA Nisbet (eds). Contemporary Social Problems. New York : Harcourt, Brace & World, 1961.
- 4 Janis I, Mann L. Decision Making: A Psychological Analysis of Conflict, Choice and Commitment. New York : Free Press, 1977.
- 5 Lindell MK, Perry RW. Behavioral Foundations of Community Emergency Planning. Washington , DC : Hemisphere Press, 1992.
- 6 Mileti DS, Drabek T, Haas JE. Human Systems in Extreme Environments. Boulder , CO : University of Colorado Institute of Behavioral Science, 1975.
- 7 Mileti DS, Peek L. The social psychology of public response to warnings of a nuclear power plant accident. Journal of Hazardous Materials, 2000; 75: 181–194.
- 8 Mileti, D S, Sorensen JH. Why people take precautions against natural disasters. Pp. 296–320 in N Weinstein (ed). Taking Care: Why People Take Precautions. New York : Cambridge University Press, 1987.
- 9 Perry RW, Lindell MK, Greene MR. Evacuation Planning in Emergency Management. Lexington , MA : Heath Lexington Books, 1981.
- 10 Tierney K, Lindell, MK, Perry RW. Facing the Unexpected: Disaster Preparedness and Response in the United States. Washington , DC : Joseph Henry Press, 2001.
- 11 Burton I, Kates, R, White GF. The Environment as Hazard, 2nd edition. New York : Guildford Press, 1993.
- 12 Lindell MK, Alesch D, Bolton PA, Greene MR, Larson LA, Lopes R, May PJ, Mulilis J-P, Nathe S, Nigg JM, Palm R, Pate P, Perry RW, Pine J, Tubbesing SK, Whitney DJ. Adoption and implementation of hazard adjustments. International Journal of Mass Emergencies and Disasters Special Issue, 1997; 15: 327–453. Available at: http://www.ijmed.org, Accessed 1 May 2010.
- 13 Lindell MK, Perry RW. Communicating Environmental Risk in Multiethnic Communities. Thousand Oaks , CA : Sage, 2004.
- 14 Gladwin CH, Gladwin H, Peacock WG. Modeling hurricane evacuation decisions with ethnographic methods. International Journal of Mass Emergencies and Disasters, 2001; 19: 117–143. Available at: http://www.ijmed.org, Accessed 1 May 2010.
- 15 Perry RW, Greene, M. Citizen Response to Volcanic Eruptions. New York : Irvington, 1983.
- 16 Lindell MK, Prater CS, Perry RW. Fundamentals of Emergency Management. Emmitsburg , MD : Federal Emergency Management Agency Emergency Management Institute, 2006. Available at: http://www.training.fema.gov/EMIWeb/edu/fem.asp, Accessed 1 May 2010.
- 17 Lasswell H. The structure and function of communication in society. Pp. 43–71 in L Bryson (ed). Communication of Ideas. New York : Harper, 1948.
- 18 McGuire WJ. The nature of attitudes and attitude change. Pp. 329–334 in G Lindsey, E Aronson (eds). Handbook of Social Psychology, 2nd edition. Reading , MA : Addison-Wesley, 1969.
- 19 McGuire WJ. The nature of attitudes and attitude change. Pp. 233–256 in G Lindsey, E Aronson (eds). Handbook of Social Psychology, 3rd edition. New York : Random House, 1985.
- 20 O'Keefe D. Persuasion: Theory and Research, 2nd edition. Thousand Oaks , CA : Sage, 2002.
- 21 Petty RE, Wegener DT. Attitude change: Multiple roles for persuasion variables. Pp. 323–390 in DT Gilbert, ST Fiske, G Lindzey (eds). Handbook of Social Psychology, 4th edition. New York : McGraw-Hill, 1998.
- 22 Lindell MK, Prater CS, Peacock WG. Organizational communication and decision making in hurricane emergencies. Natural Hazards Review, 2007; 8: 50–60.
- 23 Rogers GO, Sorensen JH. Diffusion of emergency warnings. Environmental Professional, 1988; 10: 185–198.
- 24 Aguirre BE. The lack of warnings before the Saragosa tornado. International Journal of Mass Emergencies and Disasters, 1988; 6: 65–74. Available at: http://www.ijmed.org, Accessed 1 May 2010.
- 25 Baker EJ. Hurricane evacuation behavior. International Journal of Mass Emergencies and Disasters, 1991; 9: 287–310. Available at: http://www.ijmed.org, Accessed 1 May 2010.
- 26 Fiske ST, Taylor SE. Social Cognition: From Brains to Culture. Boston : McGraw-Hill, 2008.
- 27 Committee on Disaster Research in the Social Sciences. Facing Hazards and Disasters: Understanding Human Dimensions. Washington , DC : National Academy of Sciences/National Research Council, 2006.
- 28 Mayhorn CB. Cognitive aging and the processing of hazard information and disaster warnings. Natural Hazards Review, 2005; 6: 165–170.
- 29 Lindell MK, Prater CS. Tsunami preparedness on the Oregon and Washington coast: Recommendations for research. Natural Hazards Review, 2010; 11: 69–81.
- 30 Turner R, Nigg J, Heller-Paz D. Waiting for Disaster. Los Angeles : University of California Press, 1986.
- 31 Morgan MG, Fischhoff B, Bostrom A, Atman CJ. Risk Communication: A Mental Models Approach. Cambridge : Cambridge University Press, 2002.
- 32 Slovic P, Fischhoff B, Lichtenstein S. How safe is safe enough: A psychometric study of attitudes toward technological risks and benefits. Pp. 80–103 in P Slovic (ed). The Perception of Risk. London : Earthscan, 1980.
- 33 Terpstra T, Lindell MK, Gutteling JM. Does communicating (flood) risk affect (flood) risk perceptions? Results of a quasi-experimental study. Risk Analysis, 2009; 29: 1141–1155.
- 34 Lindell MK, Prater CS. Household adoption of seismic hazard adjustments: A comparison of residents in two states. International Journal of Mass Emergencies and Disasters, 2000; 18: 317–338. Available at: http://www.ijmed.org, Accessed 1 May 2010.
- 35 Sorensen JH. Hazard warning systems: Review of 20 years of progress. Natural Hazards Review, 2000; 1: 119–125.
- 36 Lindell MK. North American cities at risk: Household responses to environmental hazards. In. T Rossetto, H Joffe, J Adams (eds). Cities at Risk: Living with Perils in the 21st Century. Dordrecht : Springer, in press.
- 37 Mileti DS, Fitzpatrick C. The causal sequence of risk communication in the Parkfield earthquake prediction experiment. Risk Analysis, 1992; 12: 393–400.
- 38 Dash N, Gladwin H. Evacuation decision making and behavioral responses: Individual and household. Natural Hazards Review, 2007; 8: 69–77.
- 39 Terpstra T, Gutteling JM. Households’ perceived responsibilities in flood risk management in the Netherlands. International Journal of Water Resources Development, 2008; 24: 555–565.
- 40 Perry RW, Lindell MK. Volcanic risk perception and adjustment in a multi-hazard environment. Journal of Volcanology and Geothermal Research, 2008; 172: 170–178.
- 41 Lindell MK, Whitney DJ. Correlates of seismic hazard adjustment adoption. Risk Analysis, 2000; 20: 13–25.
- 42 Mileti DS, Darlington JD. The role of searching in shaping reactions to earthquake risk information. Social Problems, 1997; 44: 89–103.
- 43 Ge Y, Peacock WG, Lindell MK. Florida households’ expected responses to hurricane hazard mitigation incentives. Risk Analysis, in press.
- 44 Lindell MK, Hwang SN. Households’ perceived personal risk and responses in a multi-hazard environment. Risk Analysis, 2008; 28: 539–556.
- 45 Weinstein ND. Effects of personal experience on self-protective behavior. Psychological Bulletin, 1989; 105: 31–50.
- 46 Palm R, Hodgson M, Blanchard, RD, Lyons D. Earthquake Insurance in California. Boulder , CO : Westview Press, 1990.
- 47 Peacock WG, Brody SD, Highfield W. Hurricane risk perceptions among Florida's single family homeowners. Landscape and Urban Planning, 2005; 73: 120–135.
- 48 Preston V, Taylor SM, Hedge DC. Adjustment to natural and technological hazards: A study of an urban residential community. Environment and Behavior, 1983; 15: 143–164.
- 49 Lindell MK, Earle TC. How close is close enough: Public perceptions of the risks of industrial facilities. Risk Analysis, 1983; 3: 245–253.
- 50 Arlikatti S, Lindell MK, Prater CS, Zhang Y. Risk area accuracy and hurricane evacuation expectations of coastal residents. Environment and Behavior, 2006; 38: 226–247.
- 51 Zhang Y, Prater CS, Lindell MK. Risk area accuracy and evacuation from Hurricane Bret. Natural Hazards Review, 2004; 5: 115–120.
- 52 Lindell MK, Perry RW. Household adjustment to earthquake hazard: A review of research. Environment and Behavior, 2000; 32: 590–630.
- 53 Fishbein MF, Ajzen I. Predicting and Changing Behavior: The Reasoned Action Approach. New York : Psychology Press, 2010.
- 54 Mulilis J-P, Duval TS. Negative threat appeals and earthquake preparedness: A person-relative-to-event PrE model of coping with threat. Journal of Applied Social Psychology, 1995; 25: 1319–1339.
- 55 Kunreuther H, Ginsberg R, Miller L, Sagi P, Slovic P, Borkan B, Katz N. Disaster Insurance Protection: Public Policy Lessons. New York : John Wiley, 1978.
- 56 Davis MS. Living along the fault line: An update on earthquake awareness and preparedness in Southern California. Urban Resources, 1989; 5: 8–14.
- 57 Russell L, Goltz JD, Bourque LB. Preparedness and hazard mitigation actions before and after two earthquakes. Environment and Behavior, 1995; 27: 744–770.
- 58 Lindell MK, Arlikatti S, Prater CS. Why people do what they do to protect against earthquake risk: Perceptions of hazard adjustment attributes. Risk Analysis, 2009; 29: 1072–1088.
- 59 Lindell MK, Prater CS. Risk area residents’ perceptions and adoption of seismic hazard adjustments. Journal of Applied Social Psychology, 2002; 32: 2377–2392.
- 60 Terpstra T, Lindell MK. Citizens’ Perceptions of Flood Hazard Adjustments: An Application of the Protective Action Decision Model. College Station , TX : Texas A&M University Hazard Reduction & Recovery Center, 2009.
- 61 Pijawka KD, Mushkatel AH. Public opposition to the siting of the high-level nuclear waste repository: The importance of trust. Policy Studies Review, 1991; 10: 180–194.
- 62 Lang JT, Hallman WK. Who does the public trust? The case of genetically modified food in the United States. Risk Analysis, 2005, 25: 1241–1252.
- 63 French JRP, Raven BH. The bases of social power. Pp. 150–167 in D Cartwright (ed). Studies in Social Power. Ann Arbor , MI : Institute for Social Research, 1959.
- 64 Raven B. Social influence and power. Pp. 371–382 in I Steiner, M Fishbein (eds). Current Studies in Social Psychology. New York : Holt, Rinehart & Winston, 1965.
- 65 Raven BH. The bases of power: Origins and recent developments. Journal of Social Issues, 1993; 49: 227–251.
- 66 Eagly AH, Chaiken S. The Psychology of Attitudes. Ft. Worth , TX : Harcourt, Brace College Publishers, 1993.
- 67 Arlikatti S, Lindell MK, Prater CS. Perceived stakeholder role relationships and adoption of seismic hazard adjustments. International Journal of Mass Emergencies and Disasters, 2007; 25: 218–256. Available at: http://www.ijmed.org, Accessed 1 May 2010.
- 68 Meyer P. Defining and measuring credibility of newspapers: Developing an index. Journalism Quarterly, 1988; 65: 567–574, 588.
- 69 Jackson EL. Response to earthquake hazard: The West Coast of North America. Environment and Behavior, 1981; 13: 387–416.
- 70 Garcia EM. Earthquake preparedness in California: A survey of Irvine residents. Urban Resources, 1989; 5: 15–19.
- 71 Mulilis JP, Duval TS. The PrE model of coping with threat and tornado preparedness behavior: The moderating effects of felt responsibility. Journal of Applied Social Psychology, 1997; 27: 1750–1766.
- 72 Lazarus RS, Folkman S. Stress, Appraisal, and Coping. New York : Springer, 1984.
- 73 Mileti DS. Natural hazards warning systems in the United States. Boulder , CO : University of Colorado Institute of Behavioral Science, 1975.
- 74 Perry RW. Evacuation decision making in natural disaster. Mass Emergencies, 1979; 4: 25–38.
- 75 Perry RW, Hirose H. Volcano Management in the United States and Japan. Greenwich , CT : JAI Press, 1991.
- 76 Blanchard-Boehm RD. Understanding public response to increased risk from natural hazards. International Journal of Mass Emergencies and Disasters, 1998; 16: 247–278. Available at: http://www.ijmed.org, Accessed 1 May 2010.
- 77 Houts PS, Cleary PD, Hu TW. The Three Mile Island Crisis: Psychological, Social and Economic Impacts on the Surrounding Population. University Park , PA : Pennsylvania State University Press, 1988.
- 78 Perry RW. Comprehensive Emergency Management: Evacuating Threatened Populations. Greenwich , CT : JAI, 1985.
- 79 Fritz CE, Marks, E. The NORC studies of human behavior in disaster. Journal of Social Issues, 1954; 10: 26–41.
- 80 Perry RW. Environmental hazards and psychopathology. Environmental Management, 1983; 7: 543–552.
- 81 Withey S. Reaction to uncertain threat. Pp. 93–123 in G Baker, D Chapman (eds). Man and Society in Disaster. New York : Basic Books, 1962.
- 82 Lindell MK, Lu JC, Prater CS. Household decision making and evacuation in response to Hurricane Lili. Natural Hazards Review, 2005; 6: 171–179.
- 83 Lindell MK, Prater CS. A hurricane evacuation management decision support system (EMDSS). Natural Hazards, 2007; 40: 627–634.
- 84 Huang SK, Lindell MK, Prater CS, Wu HC, Siebeneck LK. Household Evacuation Decision Making in Response to Hurricane Ike. College Station , TX : Texas A&M University Hazard Reduction & Recovery Center, 2010.
- 85 Lindell MK, Mumpower J, Huang S-K, Wu H-C. Perceptions and Expected Responses to a Water Contamination Emergency. College Station , TX : Texas A&M University Hazard Reduction & Recovery Center, 2010.
- 86 Lindell MK, Kang JE, Prater CS. The logistics of household evacuation in Hurricane Lili. Natural Hazards, in press.
- 87 Fu H, Wilmot CG, Zhang H, Baker EJ. Modeling the hurricane evacuation response curve. Transportation Research Record, 2007; 2022: 94–102.
- 88 Baker EJ. Hurricane evacuation in the United States. Pp. 98–108 in R Pielke, R Pielke (eds). Storms, Vol .1. London : Routledge, 2000.
- 89 Dow K, Cutter SL. Crying wolf: Repeat responses to hurricane evacuation orders. Coastal Management, 1998; 26: 237–252.
- 90 Dow K, Cutter SL. Emerging hurricane evacuation issues: Hurricane Floyd and South Carolina. Natural Hazards Review, 2002; 3: 12–18.
- 91 Southern California Earthquake Center. Uniform California Earthquake Rupture Forecast (UCERF), 2011. Available at: http://www.scec.org/ucerf/, Accessed 27 January 2011.
- 92 Hanson S, Vitek JD, Hanson PO. Natural disaster: Long-range impact on human response to future disaster threats. Environment and Behavior, 1979; 11: 268–284.
- 93 Drabek TE. Social processes in disaster: Family evacuation. Social Problems, 1969; 16: 336–347.
- 94 Lindell MK, Perry RW. Risk area residents’ changing perceptions of volcano hazard at Mt. St. Helens. Pp. 159–166 in F Siccardi, J Nigg, J Nemec (eds). Prediction and Perception of Natural Hazards. Amsterdam : Kluwer Academic Publishers, 1993.
- 95 Drabek TE, Stephenson J. When disaster strikes. Journal of Applied Social Psychology, 1971; 1: 187–203.
- 96 Morss RE, Hayden MH. Storm surge and “certain death”: Interviews with Texas coastal residents following Hurricane Ike. Weather, Climate, and Society, 2010; 2: 174–189.
- 97 Perry RW, Lindell MK, Greene MR. Threat perception and public response to volcano hazard. Journal of Social Psychology, 1982; 116: 199–204.
- 98 Triandis HC. Values, attitudes, and interpersonal behavior. Pp. 195–259 in H Howe, M Page (eds). Nebraska Symposium on Motivation, Vol. 27. Lincoln , NE : University of Nebraska Press, 1980.
- 99 Heath SE, Kass PH, Beck AM, Glickman LT. Human and pet-related risk factors for household evacuation failure during a natural disaster. American Journal of Epidemiology, 2001; 153; 659–667.
- 100 Van Willigen M, Edwards T, Edwards B, Hessee S. Riding out the storm: Experiences of the physically disabled during Hurricanes Bonnie, Dennis, and Floyd. Natural Hazards Review, 2002; 3: 98–106.
- 101 Killian LM. The significance of multi-group membership in disaster. American Journal of Sociology, 1952; 57: 309–314.
- 102 Drabek TE, Boggs K. Families in disaster: Reactions and relatives. Journal of Marriage and the Family, 1968; 30: 443–451.
- 103 Weinstein ND, Rothman AJ, Sutton SR. Stage theories of health behavior: Conceptual and methodological issues. Health Psychology, 1998; 17: 290–299.
- 104 Prochaska JO, Johnson S, Lee P. The transtheoretical model of behavior change. Pp. 59–84 in DS Gochman (ed). Handbook of Health Behavior Research I: Personal and Social Determinants. New York : Plenum Press, 1997.
- 105 Weinstein ND. The precaution adoption process. Health Psychology, 1988; 7: 355–386.
- 106 Birkland TA. After Disaster: Agenda Setting, Public Policy and Focusing Events. Washington , DC : Georgetown University Press, 1997.
- 107 Petty RE, Wegener DT. The elaboration likelihood model: Current status and controversies. Pp. 37–72 in Chaiken, Y Trope (eds). Dual-Process Theories in Social Psychology. New York : Guilford Press, 1999.
- 108 Floyd DL, Prentice-Dunn S, Rogers RW. A meta-analysis of research on protection motivation theory. Journal of Applied Social Psychology, 2000; 30: 407–429.
- 109 Neuwirth K, Dunwoody S, Griffin RJ. Protection motivation and risk communication. Risk Analysis, 2000; 20: 721–734.
- 110 Rogers RW. A protection motivation theory of fear appeals and attitude change. Journal of Psychology, 1975; 91: 93–114.
- 111 Lindell MK. Perceived characteristics of environmental hazards. International Journal of Mass Emergencies and Disasters, 1994; 12: 303–326. Available at: http://www.ijmed.org, Accessed 1 May 2010.
- 112 Whitney DJ, Lindell MK, Nguyen DH. Earthquake beliefs and adoption of seismic hazard adjustments. Risk Analysis, 2004; 24: 87–102.
- 113 Bostrom A, Lofstedt RE. Nanotechnology risk communication past and prologue. Risk Analysis, 2010; 30: 1645–1662.
- 114 Scott WA, Osgood DW, Peterson C. Cognitive Structure: Theory and Measurement of Individual Differences. New York : Wiley, 1979.
- 115 Converse PE. The nature of belief systems in mass publics. Pp. 206–261 in DE Apter (ed). Ideology and Discontent. New York : Free Press, 1964.
- 116 Schuman H, Kalton G. Survey methods. Pp. 635–698 in G Lindzey, E Aronson (eds). The Handbook of Social Psychology, 3rd edition, Vol. 1. Reading , MA : Addison-Wesley, 1985.
- 117 Dooley D, Catalano R, Mishra S, Serxner S. Earthquake preparedness: Predictors in a community survey. Journal of Applied Social Psychology, 1992; 22: 451–470.
- 118 Seeger MW, Sellnow TL, Ulmer RR. Communication and Organizational Crisis. Westport , CT : Praeger, 2003.
- 119 Lindell MK. EMBLEM2: An empirically based large-scale evacuation time estimate model. Transportation Research, 2008; A 42: 140–154.
- 120 Lindell MK, Prater CS. Critical behavioral assumptions in evacuation analysis for private vehicles: Examples from hurricane research and planning. Journal of Urban Planning and Development, 2007; 133: 18–29.
- 121 Lindell MK, Perry RW. Warning mechanisms in emergency response systems. International Journal of Mass Emergencies and Disasters, 1987; 5: 137–153. Available at: http://www.ijmed.org, Accessed 1 May 2010.
- 122 Gladwin H, Peacock WG. Warning and evacuation: A night for hard houses. Pp. 52–74 in WG Peacock, BH Morrow, H Gladwin (eds). Hurricane Andrew: Gender, Ethnicity and the Sociology of Disasters. London : Routledge, 1997.
- 123 Dixit VV, Pande A, Radwan E, Abdel-Aty M. Understanding the impact of a recent hurricane on mobilization time during a subsequent hurricane. Transportation Research Record, 2008; 2041: 49–57.
- 124 Fu H, Wilmot CG. Survival analysis–based dynamic travel demand models for hurricane evacuation. Transportation Research Record, 2006; 1964: 211–218.
- 125 Wilmot CG, Mei B. Comparison of alternative trip generation models for hurricane evacuation. Natural Hazards Review, 2004; 5: 170–178.
- 126 Siebeneck LK, Cova TJ. An assessment of the return-entry process for Hurricane Rita 2005. International Journal of Mass Emergencies and Disasters, 2008; 26: 91–111. Available at: http://www.ijmed.org, Accessed 1 May 2010.
- 127 Norris FH, Smith T, Kaniasty K. Revisiting the experience-behavior hypothesis: The effects of Hurricane Hugo on hazard preparedness and other self-protective acts. Basic and Applied Social Psychology, 1999; 21: 37–47.
- 128 Petty RE, Cacioppo JT. Communication and Persuasion: Central and Peripheral Routes to Attitude Change. New York : Springer-Verlag, 1986.
- 129 Chaiken S. The heuristic model of persuasion. Pp. 3–39 in MP Zanna, JM Olson, CP Herman (eds). Social Influence: The Ontario Symposium, Vol. 5. Hillsdale NJ : Erlbaum, 1987.
- 130 Knabb RD, Rhome JR, Brown DP. Tropical Cyclone Report: Hurricane Katrina 23–30 August 2005. Mimi , FL : National Hurricane Center, 2006. Available at: http://www.nhc.noaa.govpdf/TCR-AL122005_Katrina.pdf, Accessed 25 January 2011.
- 131 Burton L, Hicks MJ. Hurricane Katrina: Preliminary Estimates of Commercial and Public Sector Damages. Huntington , WV : Marshall University for Economic and Business Research, 2005. Available at: http://www.marshall.edu/cber/, Accessed 1 January 2011.