Chapter 13 : Single Sample t-Test Flashcards Preview

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Flashcards in Chapter 13 : Single Sample t-Test Deck (26):

When do you use the Z-test?(2)

-When the mean and standard deviation of the null-hypothesis population are KNOWN.
- Usually you will only have the mean.


When population standard deviation is UNKOWN what test do you use?

- t-Test


What are the three kinds of t-tests?

- Single Sample t-Test
- Correlated samples t-Test
- Independent Samples t-Test


What is the t-test formula, what data does it involve??????Difference with z-test?

- Tobt= Xobt- u/ Sx
**Sx= standard error of sample…
- Z formula uses POPULATION data not sample


Probability distribution of t-values:
- variation in t values?
- Probability ?

- different possible t values for samples of a given N
- Probability of getting each value if sampling is random from the null hypothesis population.


Characteristics of Sampling distribution of T ?
- shaped similarly to z distribution if: (2)

-Sample size X >/= 30
-If Ho population is normally distributed


There is a different curve for each ___(_).

- sample size (N)


What are Degrees of freedom? (df)
- When is this the most relevant ?

- number of scores that are free to vary in calculating any statistic.
- Most relevant when dealing with standard deviation.


What is the formula for the sum of deviations about the mean?

s = \/E(X-Xbar)^2/N-1


What is the formula for Xbar?

Xbar= EX/N


T and Z distributions are both ____ at zero. As the df increases, t becomes __ similar to z. As df approaches infinity, t becomes ____ to z. At any value of df ___.

- symmetrical
- more
- Tcrit>Zcrit


Steps to solving single sample t-test problems?

1. solve for tobt
2. find the df
3. find tcrit on table D using Df and alpha
4. If | tobt |>| tcrit |, reject Ho


What is the formula for calculating Tobt directly from raw scores? Benefit?

- Tobt= Xbar obt - u/ >/SS/N(N-1)
- no need to calculate S


What does the IB has a real effect mean?

- Tobt is greater than Tcrit
- rejected Ho


What is the magnitude of the real effect?

- statistical significance vs practical significance.


Measures of effect size are calculated using what?

- Cohen's d


Cohen's d is?(2)

- relationship between mean difference and effect size, Mean diff= Xobt-u
- main interest is magnitude..absolute value!


Choen's d is _____. Divided by the __ standard deviation.

- standardized, sample


What is the computational equation for effect size for single sample T-tests?

- d= | xobt- u |/ s

Xobt= sample mean
u= population mean
s= sample standard deviation
d= estimated d


Often the ___ mean is unknown. We use the __ mean to estimate the ___ mean.

- population
- sample
- population


Point estimate??

- uses only one value to estimate population mean


Interval estimate??

- uses a range of values to estimate population mean


What are confidence intervals?
Confidence limits?

- range of values which probably contain the population mean.
- values that bound the confidence interval
u lower= Xobt- Sxtcrit (Sx = s/ >/N)
u upper= Xobt + Sxtcrit
- can be CI of 95% or 99%


-If the confidence interval is 99% what is the range?
-what of 95%?

- -t 0.025 <= t 0.005


List the steps to solving for a confidence interval!

1. find Sx
2. examine alpha, if it's one or two tail,
3. find df
4. Solve for the lower and upper limits
5. conclude with the interval.


How is a proper conclusion for confidence intervals worded?

- The probability is ___ that the interval contains the population mean.