Standard Deviation: How to Determine if You Have the Population or Sample Standard Deviation
Reading each problem very carefully will help you determine if the population standard
deviation or the sample standard deviation is being given. Sometimes the pr
Psychology 1110 Midterm Exam - Dr. Joan Wigal
Elementary Statistical Reasoning - Online
You are allowed to have your textbooks, assignments, Instruction Materials, and any notes (and
tables) with you, as well as a calculator. However, you are not allowed
Confidence Intervals and the NEW Critical Value
For confidence intervals, we need to find a new critical value. For example, if you are asked to
find the new critical value for the 99% confidence interval, you would use The Normal
Distribution (z) table i
The Fair Trade Alternative
A Social Justice Issue in Less
Why do producers need Fair Trade?
The Case of Coffee
Over 50% grown by small scale farmers
Lack of direct access to the market
(dependency on middlemen)
Brazil in the Global
Review of Core-Periphery
Is Brazil a core or periphery
What characteristics should we
expect Brazil to have?
Brazil is the FIFTH largest country
in the world (area, population).
Which 4 countries are lar
Calculating the 95% and 99% Confidence Intervals
Let's use the 95% and 99% confidence interval examples in the course notes:
The formula is as follows:
Mean of the sample + (t or z critical value)(sample standard deviation / square root of n)
When to perform a z test vs. a t test
=> Under what circumstances do we use a t test? A z test? Please see page 6 of the course
notes: When the population standard deviation is unknown, it has to be estimated by using the
sample standard deviation(s). So
One-Tailed vs. Two-Tailed Tests
Remember that, in looking at the differences between the two groups, if the researcher is
trying to determine if there is an improvement or an increase in the dependent variable being
measured (or a deterioration or a decre
Finding the Critical Value
We only divide alpha by 2 when we are using the table to look up the critical value for a twotailed z test - but not for a one-tailed z test. For example, the critical z value for a two-tailed z
test with an alpha level of .05 i
Should the Critical z (or t) Value be Positive or Negative?
Is the critical z (or t) value + or - ?
The critical value can either be + or -, depending on the direction of the hypothesis . . . for
example, a two-tailed test that only hypothesizes a differe
THE NULL (H0) IS ACTUALLY TRUE
NULL (H0) IS ACTUALLY FALSE
Type 1 error
P = 1 - = Power
Fail to Reject H0
Type 2 error
1. A woman is found guilty but she is actually innocent. This is an
Type 1 and Type 2 Errors
The null hypothesis states that there is no difference.
A Type 1 error is possible when a researcher has rejected the null hypothesis - and determined
that there actually IS a difference - when the null hypothesis is actually true
The null hypothesis - and its opposite, the alternative hypothesis - are the conclusions that we state
after performing a z-test or a t-test and determining whether or not a difference between groups exists.
The hypotheses are our stated conclu
DOES THE DESCRIPTION OF THE EXPERIMENT.
hypothesize that there will be an increase or decrease? Or simply a difference?
If a difference:
- the test is two-tailed
- the symbol is = to the population mean for the null hypothesis
- the symbol is to the popul
Calculating the Standard Error and Sampling Distribution of the Mean
Central Limit Theorem- Given a population with a mean () and variance (2), the sampling
distribution of the mean will have a mean equal to and a variance equal to 2 / N (which is the
December 31, 2015
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