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Research Methods in AD/PR

2007 Fall_COMM 420_Week 4(1) @ NY. Research Methods in AD/PR. COMM 420 Section 8 Tuesday / Thursday 3:35 pm -5:30 pm 143 Stuckeman Nan Yu. 2007 Fall_COMM 420_Week 4(1) @ NY. Population. “Parameter” Census If you question every member of the population Universe Words, news, characters.

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Research Methods in AD/PR

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  1. 2007 Fall_COMM 420_Week 4(1) @ NY Research Methods in AD/PR COMM 420 Section 8 Tuesday / Thursday 3:35 pm -5:30 pm143 Stuckeman Nan Yu

  2. 2007 Fall_COMM 420_Week 4(1) @ NY Population • “Parameter” • Census • If you question every member of the population • Universe • Words, news, characters

  3. 2007 Fall_COMM 420_Week 4(1) @ NY Sample Can a small group of people represent a larger population? Yes, but we need to make the sample representative.

  4. 2007 Fall_COMM 420_Week 4(1) @ NY Sample A sample is a representative group of people similar to the population.

  5. 2007 Fall_COMM 420_Week 4(1) @ NY Sampling • Sampling: the process of choosing your sample • Goal • To ensure the sample are representative of the target population. • To reduce selection bias

  6. 2007 Fall_COMM 420_Week 4(1) @ NY Two types of sampling • Probability sampling • Non-probability sampling

  7. 2007 Fall_COMM 420_Week 4(1) @ NY Probability Sampling (ideal) • Requirements • Every person in the population should have an equal chance of being chosen. • No one will be excluded due to any reasons. • Every one in the population has a specific and known probability of being included in your sample.

  8. 2007 Fall_COMM 420_Week 4(1) @ NY Probability Sampling What is the probability of selecting a ball in the box? 1/10=10%

  9. 2007 Fall_COMM 420_Week 4(1) @ NY Probability Sampling If a red ball is selected and taken out of the box, what is the probability of selecting another ball in the box? 1/9=11.1%

  10. 2007 Fall_COMM 420_Week 4(1) @ NY Probability Sampling If another blue ball is selected and taken out of the box, what is the probability of selecting a ball in the box? 1/8=12.5%

  11. 2007 Fall_COMM 420_Week 4(1) @ NY Probability Sampling As we select more and more balls and take them out of the boxes, the probability of selecting a ball has increased. 1/10=10% 1/9=11.1% 1/8=12.5%

  12. 2007 Fall_COMM 420_Week 4(1) @ NY Against the rule! Probability Sample — • Every one in the population has a specific and known probability of being included in your sample.

  13. 2007 Fall_COMM 420_Week 4(1) @ NY So, what we should do is… We take one ball out, put it back, mix them up, then, draw another ball… So the probability of selecting one ball is always 1/10=10%

  14. 2007 Fall_COMM 420_Week 4(1) @ NY Probability Sample Every person in the population should have an equal chance of being chosen.

  15. 2007 Fall_COMM 420_Week 4(1) @ NY Types of probability sampling • Simple random sampling An ideal situation that researchers always try to achieve With this method, each member of the population has a statistically equal chance of being selected as a sample, thus reducing bias in the sample.

  16. 2007 Fall_COMM 420_Week 4(1) @ NY Types of probability sampling • Stratified Random Sampling • Very often used in political opinion polls, they will break down the population first by • Sex • Age • Race • …… • Then random select people from each group.

  17. 2007 Fall_COMM 420_Week 4(1) @ NY Types of probability sampling • Systematic Random Sampling • #2, #10 on each page of a telephone book • opinion page of the New York Times on every Mondays and Thursdays from 2003-2007

  18. 2007 Fall_COMM 420_Week 4(1) @ NY Non-probability sample • Not everyone in the population has an equal chance to be chosen. • We choose people that we think match the population characteristics.

  19. 2007 Fall_COMM 420_Week 4(1) @ NY Types • Convenience sample • Limitations of times/resources. • Sampling whoever you can get conveniently. • This approach is commonly used in the academic-orientated studies, but not in the real-world research. • Location biases, time biases,…etc.

  20. 2007 Fall_COMM 420_Week 4(1) @ NY Types • Quota sampling • The population is first segmented into mutually exclusive sub-groups • Then choose subjects or units from each segment based on a specified proportion. • If in a population, 80% are female, 20% are male. You need to make sure that the sample that you create follow the similar proportion.

  21. 2007 Fall_COMM 420_Week 4(1) @ NY Volunteer Sampling • Participants are rewarded in some way. • Class credit • Money… • Motivation biased, location biased…

  22. 2007 Fall_COMM 420_Week 4(1) @ NY How to contact your participations • Telephone • Mail • Face-to-face, door-to-door • Online questionnaires • Computerized telephone

  23. 2007 Fall_COMM 420_Week 4(1) @ NY Sampling size and error • Sampling error may introduced by • the process itself • biases • It may be reduced by increasing the sample size. • By reducing the sampling error, we are trying to make the sample as representative as possible.

  24. 2007 Fall_COMM 420_Week 4(1) @ NY Video Time • Sampling and Estimation • Deadly Deception

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