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It allows us to accurately infer characteristics about a population. Its cheap and fast. |
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Data gathered from an entire population |
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A selection of events from a population |
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A group defined by the researcher |
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The tendency for a sample to be wrong so it doesn't represent the population accurately |
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1) Must represent the population accurately. 2) Must be large enough to permit accurate analysis of the data they gather |
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Sample size: how large should a sample be? |
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Depends on how much sampling error (bias) you are willing to tolerate |
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Sampling error. what is it? |
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margin of error associated with the sample |
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Good reporting of a survey has it. it is the % Chance its completely wrong |
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Statistical effects of small samples |
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1) Small samples increase sampling error. 2) Small samples make it difficult to detect significant relationships |
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Volunteer Subjects: The 4 problems with it |
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1) Increased need for social approval. 2) Increased socioeconomic status 3) Increased intelligence 4) Tend to have reduced conformity |
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When each person in the population has an equal chance of being selected |
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True random sampling. Simple random sampling. Drawn at random. Not useful when subjects need to be divided into subgroups. used in field settings |
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Random. use when stratified group things are wanted. Problems: Have to know the size of the strata to use the info. Uses large samples = $$ |
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A way around stratified sampling. Look for naturally occurring samples in the enviro. |
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How do you sample clusters? |
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1) ID the clusters. 2) Draw random samples from the clusters. |
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Non-random sampling. Use a selection of events that a readily available. EX: Teacher uses his/her students |
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Non-random. Similar to stratified, don't take random sample. EX: Only want to study people over 6 ft tall and compare to people >5ft. tall |
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Used to study deviant (rare characteristic) behavior. Works well w/ naturally occurring events. |
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Disadvantages of snowball sampling |
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1) Yield biased results. 2) Statistically you can't compute the confidence interval. 3) Can't control the pop. 4) Refusal rate of over 25% then the info auto fails |
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3 kinds of descriptive statistics |
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1) Averages ex: avg. GPA. 2) Variability ex: compares averages. 3) Correlations ex: looks to see relationships in variability |
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Use probabilities to make inferences about populations. ex: probability it will rain tomorrow. |
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Measures of central tendency |
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Tell us whats going on in sample groups or pop's on the avg. EX: Mean, median, mode |
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Range, variance, standard deviation |
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