Flashcards in statistics Deck (10):

1

## three qualities of estimators

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1. unbiased: expected value = population parameter

2. efficient: lower standard error than other estimators

3. consistent: as n increases, estimator approaches the value of the population parameter

2

## what is most important quality of a sample?

### randomness

3

## central limit theorem

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1. M(avg of means) = M

2. std error (avg of means) = std error

3. distribution of means approaches normal as n increases, regardless of distribution of population

4

## standard error of the mean

### standard error of the sample = standard deviation of individuals / sq root of n

5

## NHST

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null hypothesis sample testing:

1. state the Ho to be tested

2. specify the acceptable risk of a type I error

3. test, then find the probability (p-value) that a sample mean will differ from the true mean by a greater amount than found in the sample (remember to count extremes at both ends, unless one-tailed)

4. make a decision about Ho: accept or reject

6

## z-test

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used when std dev of population is known (which is rare)

z=(x bar - mu)/(std dev of x)

7

## power

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1-beta. the probability of correctly rejecting Ho when it is false.

influenced by:

n

alpha

effect size

8

## t-test

###
used when std dev of population is not known. more common than z-test.

t=(xbar - mu)/(std dev of sample). use table to find t based on degrees of freedom.

9

## assumptions of independent samples t-test

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1. homogeneity of variance: variances in the population are the same (variance of X1 = variance of X2)

2. independent samples

3. random samples

4. normality: X1 and X2 are normally distributed in the populations

10