Z-scores Flashcards
When do you use a z-test and why?
To find out where a single score, or sample of scores, lie compared to the mean of the population, in standard deviation unit .
Our data has to be normally distributed and ratio or interval
Z-score formula to test an hypothesis about one score and about a sample of scores
Single score: The deviation of the score from the population mean divided by the population standard deviation.
Sample of scores: The deviation of the SAMPLE MEAN from the population mean, divided by the population standard deviation, then divided by the square root of the total sample size.
Once you have computed the z-score, what do you do
Find the p-value by looking in the z-score table for the score obtained, this will give us the p-value, then conclude
What is important to remember when calculating a z-score
First, subtract, then take that score and divide it, do not do it all at once
For a sample of scores, first calculate the square root division and then subtraction/division of that number
How is the one sample t-test different from z-test, when to use, what is the formula
T-test is used to compare scores to a population, when we know the population mean, but do not know the population’s standard deviation (z-test uses population standard deviation). The formula is the same however we replace the population standard deviation by the sample standard deviation.
Ie: formula is: Deviation from the population mean of each score, or sample mean, divided by the sample standard deviation, if sample of scores, then divided by the square root of the sample size.
After you have calculated the t value, what is the next steps?
Find degree of freedom by doing N-1
Then look on the table, find the d.f in the corresponding part either one tailed (0.100 column) or two tailed (0.05 column) depending on our hypothesis
RULE: If our calculated T VALUE is LARGER than the critical value in the table, we can reject the null hypo, and conclude a significance.
How do you report a t-test result in a report?
t(d.f) = calculated tvalue, p<0.05 or p>0.05
