AP Statistics: Unit 7 Vocabulary
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A number that describes a sample and can change from sample to sample. We often use these to estimate an unknown parameter.
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Statistic
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For an accurate result that maintains independence, the population needs to be at least 10 times as big as the sample that came from it.
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How large does a population need to be compared to the sample?
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The mean of a population (parameter)
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μ
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The proportion of a population (parameter)
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p (definition)
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The mean of a sample (Statistic)
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x̅
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The proportion of a sample (Statistic)
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p̂ (definition)
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Whenever we get a different mean from a sample; The value of a statistic varies in repeated sampling.
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Sampling Variability
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question![Calculator Notation: Y[-10,45].5](https://studyhippo.com/wp-content/uploads/2017/12/calculator-notation-y-1045-5.jpg "Calculator Notation: Y[-10,45].5")
Y minimum at -10, Y maximum at 45, counting by intervals of 5.
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Calculator Notation: Y[-10,45].5
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A parameter is unbiased IF the mean (center) of the sampling distribution is equal to the true value of the population parameter being estimated. Using this doesn't guarantee your statistics will be close to the actual value.
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Unbiased Estimator
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The larger the sample, the shorter the spread. Focus on larger samples, not more.
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Low Variability = Shorter Spread
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In most cases, the sampling distribution can be approximated by a normal curve. This depends on the sample size and the population proportion. (n and p)
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Shape
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Mean p̂ = P or the mean of a sample is the mean of a population. This happens because P-hat is an unbiased estimator of P.
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Center
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The standard deviation of p̂ gets smaller as n gets larger. This depends on both n and p.
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Spread
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the size of success in a sample over the size of the sample. X/n OR it reduces down to just p.
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p̂ =
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Mean of p̂ is p.
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Mean
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The square root of: ((P times 1-P)/n)) as long as N is greater than or equal to 10n. (the population is 10 times larger than the sample). This is on the formula sheet provided.
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Standard Deviation of p̂
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Satisfied by making sure that np is greater than or equal to 10 and n(1-p) is greater than or equal to 10.
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Large Counts Condition or 10% Condition
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Only use Normal distribution for p̂ if both conditions are true (N greater than or equal to 10n and np greater than or equal to 10)
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Rule of Thumb
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No. College board does not round the standard deviation in the multiple choice section of the test. To account for this, store the standard deviation in the x value.
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Does College Board round?
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Anything is below a 5% margin, which is most likely an error and NOT just chance.
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You should suspect a sample when...
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Standard deviation over the square root of the sample, given that N is greater than or equal to 10n.
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Standard Deviation of a mean...
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Mean is less variable and more normal. It's an unbiased estimator.
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Properties of the mean of a distribution...
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Says that when n is large (greater than 30) the sampling distribution of the sample mean is approximately normal.
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Central Limit Theorem (CLT)
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