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- 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.