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77 Cards in this Set

  • Front
  • Back
Which of these are typically used more? Population or Sample
Sample: gathering data from an entire population is usually impractical
What is assumed when collecting data for a sample
That the sample is drawn from a population of INFINITE size
What is the best way to achieve a representative sample
By selecting the sample at random
What are the different ways to do a random sampling
1)Systematic sampling
2)stratified sampling
Why is it nearly impossible to do a random sampling
Because the people still need to volunteer

Sampling Error
The amount of error in estimating a population parameter (mean, SD, etc...) from a sample

-The mean of the sample might not be exactly equal to the population, so the difference is taken (Sampling error)

Standard Error of the Mean

SEM = ?
SEM = s/sq. rt. n

s = sample standard dev.
n = sample size
-It is the estimate of how much the sample mean differs from the population mean
When Sample Size increases, what happens to the Sampling Error
it decreases

-the decrease is less noticable the larger the sample size gets

Research Hypothesis
A prediction outcome based on theoretical consideration. An informed guess

-Also known as a Scientific Hypothesis

Null Hypothesis
A statement about the numerical value of a unknown parameter

-Also known as a Statisical Hypothesis
-The hypothesis of no difference between two groups
More info

Null Hypothesis
-the hypothesis is often the reverse of what the experimenter actually believes
-Put forward to allow the data to contradict it
What is the purpose of the null hypothesis
-It is important to be able to state with confidence that the effect was really due to chance

-Hypothesis tests starts with the assumption that the effect was due to chance, that there was no difference between means of the treatment group and control
What will the number of hypotheses depend on?
The number of IV and DV
With more than one IV?
more than one hypothesis
With more than one DV?
Sometimes combined and sometimes stated separately

-Depends on the nature of the relationship between the DV's
What are some neccessities of a hypothesis in an experiment
-elements being compared should be stated
-the hypothesis should clearly describe the relationship
-hypothesis should be as concise as possible
-should understand the relationship to be tested
What are some components of a good hypothesis
-Operational hunches can be emperically assessed
-May be restated in null form
-Stated in declarative form
-Posit a relationship between variables
-Reflect a theory/body of literature
What are some components of a bad hypothesis
-refer to "differences in the DV"
-relationship and difference used in the same sentence
What are the characteristics of the Normal Curve
-Mean, Median, Mode all the same score
-Areas under the curve described by standard deviation
-Tails approach, but never touch, horizontal axis (Asymptotic)
What is the most common standard score used with a normal distribution
The Z-score

Z Score
The standardized score used to produce a normal curve with mean=0, and s=1
What does the Z score represent
-A raw score expressed in standard deviation units

z = ?
z =(X-Mean)/s
What needs to be known for the raw score to be represented as a z-score
the mean and standard deviation
What can a z-score be used to describe for a normal distribution
the percentage of the normal curve contained within 2 z-scores or a z-score and the mean
+ or - 1 sd=
+ or - 2 sd=
+ or - 3 sd=
What is an example of a standard score
a T score

Skewness (SK)=
{n/[(n-1)(n-2)]}xsum of z^3

the porportion of the time you were successful

-Also known as the p value
-statisical viewpoint: the likelihood that your results are due to chance
What is the range of probability
0 to 1

0=no way you'll be successful
1=you will win every time

-You can't have a negative probability
What is the probablility of an even?
the number of favorable outcome divided by the total number of poddible outcomes
What is a frequency distribution
the total # of scores

the number of times an event occurs of the total possible number of sample points

Sample Space
The total possible sample points
How does probability change
based on how you state what you want your successes to be
What formulas are used for determining sample spaces for statistical testing
Permutation Formulas
Combination Formulas
What is used to compute the probability of a particular score to occure
the z score and the corresponding area of the normal curve

Conditional Probability
The probability of an event given that another event has occured

an arrangement of a set of objects in which their order is considered

nPr = n!/(n-r)!

A distinct set of objects in which the order is not considered

nCr = n!/r!(n-r)!
What are Confidence Intervals
An actual estimate of the population mean and are based on a probability distribution
95%CI = ?
95%CI = Mean +or- 1.96(SEM)

SEM = s/sq.rt. n
When is it a Type I/Type II error
Decision Accept Reject

Ho True: Correct TypeI
Ho False: TypeII Correct
Type I error
True Ho Rejected

A researcher reports a difference when there is none
What is the probability called when making a Type I error
alpha level or level of significance

"the probability of observing that outcome is less than 5%"
What is the probability calles when making a Type II error
Beta and is set by Power

Power = ?
Power = 1 - beta

typically set as 0.8 meaning that the researcher is willing to take a 20% chance of making a Type II error
How can a researcher control Power
1)Increase the difference between Means
2)Decrease the Variance
3)Increase the Sample Size (easiet to control)
What will calculating the power allow us to do
To determine the number of subjects needed to have adequate POWER so as to avoid the Type II error
When is the power calculated
Once the research is complete and be based on the data from the research
What is the 7 step procedure for testing hypotheses with the one sampled z test
1)State the null hypothesis
2)Do a one sample z test
3)state the level of significance for test
4)Write the tabled critical region value
6)Compare calc. z score to critical z and make decision
7)state your conclusion
What does the one sample t test tell us
if the smaple mean is significantly different than the population mean
Why is the t distribution used (also called the Student's t distribution)
it is rarely the case that all the sample data has a perfectly normal distribution
What is the 7 step procedure of the one sampled t test
the same as the z test but using the one sample t formula in the calculations
What is assumed in the one-sampled t-test
-Normally distributed
-Interval/ratio type
-mu is known
When is the Independent t-test (or the two-sample t-test) used
when comparing 2 sample means rather than a sample mean to a population mean
What is assumed in the one-sample z-test
-Normally Distributed scores
-Interval/ratio type
-mu and sigma are know
what is assumed with an independent t-test
-Interval/ratio data
-2 independent group
-10 or more participants per group
-Equal variance
When do you have to worry about equal variances
If the group sizes are not equal, then a test for the assumption of equal variances must be tested
What is the test for equal variance called
Levene's test

-if equal, avg. the variances for the groups
-if unequal, the t calculated using seperate variances not avg.
What is the 7 step procedure for testing the hypothesis
same as before only using the two-sample t-test when calculating

CI for mean difference
95%CI= mean1 - mean2 +or- (tabled critical t)(SED)

SED = sq.rt. [(s1^2/n1)+(s2^2/n2)]
Based on the CI, when would we reject/accept the null
reject- the CI DOES NOT contain 0 in the range

accept- the CI DOES contain the 0 in the range
What is Effect size used for
used before the study to estimate the sample size
Effect Size
-calculated to see the magnitude of the difference between 2 means after the study

-helps to estimate the meaningfulness of the treatment

-used to describe the difference between the mean of the Exp. and the Cont.

-Simply a z score (Mean_e - Mean_c)/s_c
in what units is the effect size expressed in
standard deviation units
What are the two ways of evaluating the effectiveness of a treatment
1)Effect Size
2)Omega Squared
When should the Omega squared be calculated
After a t-test if a significant difference is found
Why is the Omega Squared calculated
-Gives researchers and indication of how effective the treatment variable is

-Indicates the proportion of the variance in the dependent variable that is explained by the independent variable
What does the independent t-test assume about the groups
that they are not related to each other in any way
What is it meant by using related samples
there is a single group of subjects with a dependant variable being measured on more than one occassion under more than one condition
When do we use a paired t-test
(also known as the Dependent t-test)
when the results of two different measurements depends on each other

-pairs of participants are matched on one or more characteristics and randomly placed into 2 groups
-Twin studies
What are the 7 steps procedure for testing the hypothesis
same as all the others but using a different formula
What is assumed in the dependent t-test
-two dependent samples of measures