Causes of Error in Sampling. Sampling Error Sampling error is error caused by the way you chose your...
-
Upload
horace-george -
Category
Documents
-
view
253 -
download
1
Transcript of Causes of Error in Sampling. Sampling Error Sampling error is error caused by the way you chose your...
![Page 1: Causes of Error in Sampling. Sampling Error Sampling error is error caused by the way you chose your sample – Volunteer Sampling & Convenience Sampling.](https://reader035.fdocuments.net/reader035/viewer/2022081421/56649d125503460f949e5f1a/html5/thumbnails/1.jpg)
Causes of Error in Sampling
![Page 2: Causes of Error in Sampling. Sampling Error Sampling error is error caused by the way you chose your sample – Volunteer Sampling & Convenience Sampling.](https://reader035.fdocuments.net/reader035/viewer/2022081421/56649d125503460f949e5f1a/html5/thumbnails/2.jpg)
Sampling Error
• Sampling error is error caused by the way you chose your sample– Volunteer Sampling & Convenience Sampling– Causes Bias
• How do you reduce?– Use randomness in choosing
your sample
![Page 3: Causes of Error in Sampling. Sampling Error Sampling error is error caused by the way you chose your sample – Volunteer Sampling & Convenience Sampling.](https://reader035.fdocuments.net/reader035/viewer/2022081421/56649d125503460f949e5f1a/html5/thumbnails/3.jpg)
Random Sampling Error• Random Sampling Error– You sample may randomly have a higher or lower
percentage of females, college educated people, Hispanics, etc. than what what is found in your population.
– Causes Variation• How do you reduce?– Choose a larger sample sample size.
![Page 4: Causes of Error in Sampling. Sampling Error Sampling error is error caused by the way you chose your sample – Volunteer Sampling & Convenience Sampling.](https://reader035.fdocuments.net/reader035/viewer/2022081421/56649d125503460f949e5f1a/html5/thumbnails/4.jpg)
Random Sampling Error• If your sample ≤ 10% of the population than
your error is about n =
sample size
– True no matter how big the population is• If you sampled 10,000 Indiana residents,
population 6.5 million, what is your error?
• If you sampled 10,000 South Bend residents, population 101,658 what is your error?
![Page 5: Causes of Error in Sampling. Sampling Error Sampling error is error caused by the way you chose your sample – Volunteer Sampling & Convenience Sampling.](https://reader035.fdocuments.net/reader035/viewer/2022081421/56649d125503460f949e5f1a/html5/thumbnails/5.jpg)
Random Sampling Error• If your sample ≤ 10% of the population than
your error is about n =
sample size
• If your sample ≥ 10%, then your error is better than this equation, but we won’t get into that until chapter 9.
![Page 6: Causes of Error in Sampling. Sampling Error Sampling error is error caused by the way you chose your sample – Volunteer Sampling & Convenience Sampling.](https://reader035.fdocuments.net/reader035/viewer/2022081421/56649d125503460f949e5f1a/html5/thumbnails/6.jpg)
Confidence Interval• If you calculate your error to be 1%, your
actual error could be larger. That 1% is what we call a confidence interval. You are 95% confident that the error between your measured result and the actual result is 1%.
• If the results from your study show that the percent of Americans that believe in Heaven is 88 + 5%, what that means is you are 95% confident that between 83% and 93% of the population believes in Heaven.
![Page 7: Causes of Error in Sampling. Sampling Error Sampling error is error caused by the way you chose your sample – Volunteer Sampling & Convenience Sampling.](https://reader035.fdocuments.net/reader035/viewer/2022081421/56649d125503460f949e5f1a/html5/thumbnails/7.jpg)
Undercoverage• Undercoverage is when some groups in the
population are left out of the process of choosing the sample.
• What groups CAN’T be contacted by a survey where you call random people and ask their opinion?– Amish– Homeless– People serving overseas– Prison Inmates– Unlisted numbers & other people without phones
![Page 8: Causes of Error in Sampling. Sampling Error Sampling error is error caused by the way you chose your sample – Volunteer Sampling & Convenience Sampling.](https://reader035.fdocuments.net/reader035/viewer/2022081421/56649d125503460f949e5f1a/html5/thumbnails/8.jpg)
Undercoverage• Undercoverage is when some groups in the
population are left out of the process of choosing the sample.
• How do you reduce/prevent undercoverage– Census (poll everyone)– Reduce bias in your sampling (avoid convenience
& volunteer sampling)– Stratified Sample: Split the population in groups
and then sample each group.• Example: Instead of randomly selection 100 people,
randomly select 50 men and 50 women
![Page 9: Causes of Error in Sampling. Sampling Error Sampling error is error caused by the way you chose your sample – Volunteer Sampling & Convenience Sampling.](https://reader035.fdocuments.net/reader035/viewer/2022081421/56649d125503460f949e5f1a/html5/thumbnails/9.jpg)
Nonsampling Error• Processing Error– Enter a number wrong in Excel– Math Error
• How do you reduce/prevent– Double Check your Work– Don’t Rush
![Page 10: Causes of Error in Sampling. Sampling Error Sampling error is error caused by the way you chose your sample – Volunteer Sampling & Convenience Sampling.](https://reader035.fdocuments.net/reader035/viewer/2022081421/56649d125503460f949e5f1a/html5/thumbnails/10.jpg)
Nonsampling Error• Response Error – given an incorrect response• Why would someone do that?– Lie• How much do you weigh?• Have you ever used drugs?
– Remember Incorrectly• How many minutes have you watched TV this week?• Where exactly were you at 3:30 PM last Saturday?
– Vague or Confusing Question• How many windows do you have? Do door windows
count?
![Page 11: Causes of Error in Sampling. Sampling Error Sampling error is error caused by the way you chose your sample – Volunteer Sampling & Convenience Sampling.](https://reader035.fdocuments.net/reader035/viewer/2022081421/56649d125503460f949e5f1a/html5/thumbnails/11.jpg)
Response Error• Lying causes bias• How can we reduce lying?– Confidential: the interviewer promises their name
won’t be released with the results– Anonymous: even the interviewer doesn’t know
which response sheet corresponds to which person
– Study them without them knowing, as with the handwashing homework problem• Is this ethical?
![Page 12: Causes of Error in Sampling. Sampling Error Sampling error is error caused by the way you chose your sample – Volunteer Sampling & Convenience Sampling.](https://reader035.fdocuments.net/reader035/viewer/2022081421/56649d125503460f949e5f1a/html5/thumbnails/12.jpg)
Response Error• How can we reduce memory errors?
![Page 13: Causes of Error in Sampling. Sampling Error Sampling error is error caused by the way you chose your sample – Volunteer Sampling & Convenience Sampling.](https://reader035.fdocuments.net/reader035/viewer/2022081421/56649d125503460f949e5f1a/html5/thumbnails/13.jpg)
Response Error• Confusing questions cause bias if they favor
one answer over another. They cause variability if they are just confusing in general, but don’t favor a particular outcome
• How can we reduce people from misunderstanding the question?– Clear, careful and extremely specific wording
![Page 14: Causes of Error in Sampling. Sampling Error Sampling error is error caused by the way you chose your sample – Volunteer Sampling & Convenience Sampling.](https://reader035.fdocuments.net/reader035/viewer/2022081421/56649d125503460f949e5f1a/html5/thumbnails/14.jpg)
Response Error: Question Wording• “Owning stock” means different things to a
Wall Street Banker & a Texan Rancher• 13 % of Americans think we are spending too
much on “assistance to the poor,” but 44% think we are spending too much on “welfare”
• A poll in Scotland showed that 51% would vote in favor for “independence for Scotland,” but 34% would vote in favor for “an independent Scotland separate from the United Kingdom.”
• Assistance & Independence are positive words while Welfare & Separate are negative words
![Page 15: Causes of Error in Sampling. Sampling Error Sampling error is error caused by the way you chose your sample – Volunteer Sampling & Convenience Sampling.](https://reader035.fdocuments.net/reader035/viewer/2022081421/56649d125503460f949e5f1a/html5/thumbnails/15.jpg)
Wording Questions• Loaded questions cause bias– Do you favor banning private ownership of
handguns in order to reduce the rate of violent crime?
– George Bush: great president or greatest president?
– Do you support our president?– Do you agree with all of Obama’s policies?– Do you approve or disapprove of the way Barack
Obama is handling his job as president?
![Page 16: Causes of Error in Sampling. Sampling Error Sampling error is error caused by the way you chose your sample – Volunteer Sampling & Convenience Sampling.](https://reader035.fdocuments.net/reader035/viewer/2022081421/56649d125503460f949e5f1a/html5/thumbnails/16.jpg)
Wording Questions
• Open vs. Closed Questions– Rate Obama’s performance on a scale of 1 to 10
vs. what do you think about Obama’s job as president?
– Limiting people’s options can cause bias– Limiting people’s options can reduce people
misunderstanding the question– Closed Questions are easier to analyze
![Page 17: Causes of Error in Sampling. Sampling Error Sampling error is error caused by the way you chose your sample – Volunteer Sampling & Convenience Sampling.](https://reader035.fdocuments.net/reader035/viewer/2022081421/56649d125503460f949e5f1a/html5/thumbnails/17.jpg)
Non Response
• They refuse to answer your survey. They hang up on you, slam the door in your face or just politely say no.
![Page 18: Causes of Error in Sampling. Sampling Error Sampling error is error caused by the way you chose your sample – Volunteer Sampling & Convenience Sampling.](https://reader035.fdocuments.net/reader035/viewer/2022081421/56649d125503460f949e5f1a/html5/thumbnails/18.jpg)
Nonadherer
• A nonadherer is a generic term for someone who doesn’t follow directions for whatever reason.– Example: They forgot to take the experimental pill
every 6 hours.– Example: They lied on their survey form
• How would you reduce?
![Page 19: Causes of Error in Sampling. Sampling Error Sampling error is error caused by the way you chose your sample – Volunteer Sampling & Convenience Sampling.](https://reader035.fdocuments.net/reader035/viewer/2022081421/56649d125503460f949e5f1a/html5/thumbnails/19.jpg)
Dropouts
• Sometimes your study the same person over several days, weeks, months or even years. Dropouts are people who start doing the experiment, but then stop half way through.