WELCOME TO A LESSON ON THE SOURCES OF BIAS WHEN SAMPLING A POPULATION. THERE ARE A NUMBER OF WAYS THAT A STUDY CAN BE RUINED OR BECOME INVALID BEFORE EVEN STARTING TO COLLECT DATA. WE HAVE ALREADY EXPLORED SAMPLING OR SELECTION BIAS, WHICH IS WHEN THE SAMPLE IS NOT REPRESENTATIVE OF THE POPULATION. ONE EXAMPLE OF THIS IS VOLUNTARY RESPONSE BIAS WHERE VOLUNTARY RESPONSE BIAS IS INTRODUCED BY ONLY COLLECTING DATA FROM THOSE WHO VOLUNTEER TO PARTICIPATE. THERE ARE SEVERAL OTHER POSSIBLE SOURCES OF BIAS. SO LET'S GO AHEAD AND TAKE A LOOK AT THIS LIST. WE'VE ALREADY MENTIONED THE FIRST TWO WHERE, NUMBER ONE, SAMPLING BIAS IS WHEN THE SAMPLE IS NOT REPRESENTATIVE OF THE POPULATION. TWO, VOLUNTARY RESPONSE BIAS, THE SAMPLING BIAS THAT OFTEN OCCURS WHEN THE SAMPLE IS VOLUNTEERS. THREE, SELF-INTEREST STUDY, BIAS THAT CAN OCCUR WHEN THE RESEARCHERS HAVE AN INTEREST IN THE OUTCOME. FOUR, RESPONSE BIAS, AND THIS IS A VERY BROAD CATEGORY. THIS IS WHEN THE RESPONDERS GIVE INACCURATE RESPONSES FOR ANY REASON. FIVE, PERCEIVED LACK OF ANONYMITY WHEN THE RESPONDER FEARS GIVING AN HONEST ANSWER MIGHT NEGATIVELY AFFECT THEM. SIX, LOADED QUESTIONS WHEN THE QUESTION WORDING INFLUENCES THE RESPONSES, AND SEVEN, NON-RESPONSE BIAS, WHEN PEOPLE REFUSING TO PARTICIPATE IN THE STUDY CAN INFLUENCE THE VALIDITY OF THE OUTCOME. I DO WANT TO GO BACK UP TO RESPONSE BIAS JUST FOR A MOMENT. NOTICE HOW RESPONSE BIAS COULD OCCUR BECAUSE OF NUMBER FIVE AND NUMBER SIX. AGAIN, RESPONSE BIAS IS WHEN RESPONDERS GIVE INACCURATE RESPONSES FOR ANY REASON. LET'S TAKE A LOOK AT SEVERAL EXAMPLES. A STUDY FROM A PESTICIDE COMPANY CLAIMS THAT THEIR PESTICIDES HAVE NO ENVIRONMENTAL IMPACT AND ARE COMPLETELY SAFE. THIS IS AN EXAMPLE OF A SELF-INTEREST STUDY. NOTICE HOW THE PESTICIDE COMPANY WOULD HAVE A FINANCIAL INTEREST IN THE OUTCOME OF THIS STUDY. SUCH A STUDY WOULD BE BETTER DONE BY AN INDEPENDENT THIRD PARTY. ANOTHER STUDY ASKS, "GIVEN THAT AT THE AGE OF 18 PEOPLE ARE OLD ENOUGH "TO FIGHT AND DIE FOR YOUR COUNTRY, DON'T YOU THINK THEY SHOULD BE ABLE TO DRINK ALCOHOL AS WELL?" THIS MAY YIELD A RESPONSE BIAS IN COMPARISON WITH SIMPLY ASKING, "DO YOU THINK 18-YEAR-OLDS SHOULD BE ABLE TO DRINK ALCOHOL?" SO BASED UPON HOW THIS FIRST QUESTION WAS WORDED, RESPONDERS MAY ANSWER INACCURATELY RATHER THAN THEIR TRUE FEELINGS. BUT NOTICE HOW BECAUSE OF THE BIAS IS BECAUSE OF THE WORDING OF THE QUESTION, WE COULD ALSO CLASSIFY THIS AS A LOADED OR LEADING QUESTION. ANOTHER EXAMPLE MIGHT BE IF A SAMPLE WAS ASKED, "WHEN WAS THE LAST TIME YOU ATE PIZZA?" THIS COULD LEAD TO RESPONSE BIAS IF THE PERSON CAN'T REMEMBER AND MAKES UP AN ANSWER. ANOTHER EXAMPLE OF A QUESTION THAT MIGHT HAVE RESPONSE BIAS WOULD BE, "HAVE YOU EVER CHEATED ON A TEST?" AGAIN, RESPONDERS MAY NOT RESPOND ACCURATELY FOR A VARIETY OF REASONS. RELATED TO RESPONSE BIAS IS NON-RESPONSE BIAS. THIS OCCURS WHEN A SIGNIFICANT NUMBER OF THE SAMPLE REFUSE TO ANSWER A QUESTION. IF 50% OF A SAMPLE REFUSES TO ANSWER THE QUESTION, "WHEN IS THE LAST TIME YOU READ A BOOK," THE SURVEY RESULTS FROM THIS QUESTION WOULD NOT BE REPRESENTATIVE OF THE ENTIRE POPULATION. AND AGAIN, THIS IS AN EXAMPLE OF NON-RESPONSE BIAS. A SURVEY IS CONDUCTED AT WORK AND ASKS, "WHEN IS THE LAST TIME YOU DRANK ALCOHOL?" EMPLOYEES MIGHT NOT WANT TO BE PERCEIVED AS HAVING A DRINKING PROBLEM AND GIVE AN INACCURATE ANSWER. HERE A PERCEIVED LACK OF ANONYMITY COULD INFLUENCE THE OUTCOME. NEXT, A STUDY ASKED, "DO YOU SUPPORT FUNDING RESEARCH "FOR ALTERNATIVE ENERGY SOURCES TO REDUCE A RELIANCE ON HIGH POLLUTING FOSSIL FUELS?" THIS IS AN EXAMPLE OF A LOADED OR LEADING QUESTION. AGAIN, LEADING QUESTIONS ARE QUESTIONS WITH WORDING THAT LEADS THE RESPONDENT TOWARDS AN ANSWER. WE ALSO SAW THIS EARLIER WITH THE QUESTION ABOUT WHETHER 18-YEAR-OLDS SHOULD BE ABLE TO DRINK. NOTICE LOADED OR LEADING QUESTIONS ALSO LEAD TO RESPONSE BIAS, BUT IT IS IMPORTANT TO RECOGNIZE THAT LOADED QUESTIONS CAN OCCUR INTENTIONALLY BY POLLSTERS WITH AN AGENDA OR ACCIDENTALLY THROUGH POOR QUESTION WORDING. ALSO, A CONCERN IS QUESTION ORDER WHERE THE ORDER OF QUESTIONS CAN CHANGE THE RESULTS. I HOPE YOU FOUND THIS BRIEF OVERVIEW ON THE SOURCES OF BIAS HELPFUL. THANK YOU FOR WATCHING.