5.3 Errors.

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Presentation transcript:

5.3 Errors

Sampling Frame Individuals from the population from which the sample can be obtained from. Not always the whole population. EX: A political group interested in how people in the state feel about budget cuts takes a sample of 1000 people from registered voter lists.

Errors in Sampling Undercoverage When some groups of the population are left out of the sample On purpose or by accident Examples: Call-in poll, stopping people @ mall, mailings, standing by back door of school, etc.

Processing Errors Mistakes in collecting or entering the data Examples: - doing arithmetic wrong - typos - recording wrong numbers/info - losing data

Nonresponse Error Failure to obtain data from an individual in the sample Happens because subjects refuse to respond or can’t be contacted Examples: - not answering phone/ hanging up phone - not sending back mailing - absent on day of poll - refuse to write answers on a survey

Voluntary Response Error Error from a voluntary response sample The sample is not representative of the population. Not the same as nonresponse error.

Response Error When subjects give an incorrect response Could be due to the environment, question, or person asking the questions. Examples: - lying (especially with sensitive questions) - remembering info incorrectly - don’t understand question - mislead - influenced by questions/surveyer

Wording of questions * When a question: - is confusing - uses big words or technical language that most people don’t understand - uses a word that has more than one meaning and doesn’t clarify - ARE SLANTED towards one response (based on the question alone or a statement with the question)

EXAMPLE SHEET

Complete the book problems:

p. 242 #56 56) (a) response error (b) processing error (c) undercoverage, not everyone gets the paper) p. 246 #64 64) 50% in favor was for the question worded “protecting the life of the unborn child” 29% in favor was for the question “prohibiting abortions”

p. 252 #75 75) (a) undercoverage on those not in the phone book (b) nonresponse (c) Undercoverage due to a convenience sample

Try the following: p. 253 – 256 #77 (a only), 78, 80, 81, 83

77) (a) Biased because of undercoverage 77) (a) Biased because of undercoverage. You are not able to sample the most expensive seats 78) Assign each person a number 01-30 Use a TRD and read off 2 digits at a time Ignore 00, 31-99 and repeats First 4 numbers are our sample # 19, 26, 06,09 Rodriguez, Montoya, Fernandez, Castillo

80) (a) the population is all American college students (b) the list of 340 PSY 001 students (c) If he is trying to conclude about ALL college students, you should not just sample from students in PSY 001. (d) Yes, it is slanted. “fair price to pay” (e) He did not ask students about whether they were in favor of TV commercials. He asked them if they thought commercials were a fair price to pay for watching TV. (f) No, not relevant. The sampling frame does not represent the population.

83) The wording “fight the charges” makes it seem like he is justly charged for a crime and the second question wording of “continue to serve” makes it seem like he should stay in office.