Should I use pooled or Satterthwaite?
The main difference is that the Satterthwaite approximation does not assume equal variances, whereas the pooled method does. In other words, you can always use the Satterthwaite method and be correct, but you can only use the pooled method in very specific (and rare) circumstances.
What is a pooled t-test?
The test that assumes equal population variances is referred to as the pooled t-test. Pooling refers to finding a weighted average of the two independent sample variances. The pooled test statistic uses a weighted average of the two sample variances.
What are the assumptions for pooled t-test?
The common assumptions made when doing a t-test include those regarding the scale of measurement, random sampling, normality of data distribution, adequacy of sample size, and equality of variance in standard deviation.
What is Proc Ttest in SAS?
The SAS PROC TTEST procedure is used to test for the equality of means for a two-sample (independent group) t-test.
When should an independent t-test be used?
The independent t-test is used when you have two separate groups of individuals or cases in a between-participants design (for example: male vs female; experimental vs control group).
What is Satterthwaite method?
The Satterthwaite approximation is a formula used in a two-sample t-test for degrees of freedom. It’s used to estimate an “effective degrees of freedom” for a probability distribution formed from several independent normal distributions where only estimates of the variance are known.
How do you know if data is pooled or Unpooled?
“Comparing two proportions – For proportions there consideration to using “pooled” or “unpooled” is based on the hypothesis: if testing “no difference” between the two proportions then we will pool the variance, however, if testing for a specific difference (e.g. the difference between two proportions is 0.1, 0.02, etc …
When should you use a pooled two-sample t test?
When can I use the test? You can use the test when your data values are independent, are randomly sampled from two normal populations and the two independent groups have equal variances.
When should you use a pooled two-sample t-test?
What is the difference between pooled and Unpooled t tests?
There are two versions of this test, one is used when the variances of the two populations are equal (the pooled test) and the other one is used when the variances of the two populations are unequal (the unpooled test).
What are the different types of t tests?
There are three types of t-tests we can perform based on the data at hand: One sample t-test. Independent two-sample t-test.
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Paired Sample t-test
- t = t-statistic.
- m = mean of the group.
- µ = theoretical value or population mean.
- s = standard deviation of the group.
- n = group size or sample size.
What are the 3 types of t tests?
Types of t-tests
There are three t-tests to compare means: a one-sample t-test, a two-sample t-test and a paired t-test.
What are the 3 assumptions for an independent measures t-test?
Normality. the data for each group should be approximately normally distributed. Homogeneity of variances. the variance of the outcome variable should be equal in each group.
How do you calculate Satterthwaite?
Satterthwaite Approximation
- Use the pooled standard error formula: Sp √ (1/n1 + 1/n2)
- Use Satterthwaite’s: Se = √ (s12/n1 + s22/n2)
How do you determine degrees of freedom?
To calculate degrees of freedom, subtract the number of relations from the number of observations. For determining the degrees of freedom for a sample mean or average, you need to subtract one (1) from the number of observations, n.
How do you know when to use pooled variance?
In order to run a two-sample t test, you need to decide whether you think the variances of the two groups are equal. If you think the group variances are equal, you compute the pooled variance, which estimates the common variance. You use the pooled variance estimate to compute the t statistic.
When should you use a pooled two sample t-test?
How do you know if you pooled or Unpooled?
When would you use a pooled two sample t test?
What are the 3 types of t-test?
How do I know which t-test to use?
If you are studying one group, use a paired t-test to compare the group mean over time or after an intervention, or use a one-sample t-test to compare the group mean to a standard value. If you are studying two groups, use a two-sample t-test. If you want to know only whether a difference exists, use a two-tailed test.
What is the difference between ANOVA and t-test?
The t-test is a method that determines whether two populations are statistically different from each other, whereas ANOVA determines whether three or more populations are statistically different from each other.
What is the Satterthwaite method?
How do you know how many degrees of freedom?
How do you find degrees of freedom in ANOVA?
To calculate degrees of freedom for ANOVA: Subtract 1 from the number of groups to find degrees of freedom between groups. Subtract the number of groups from the total number of subjects to find degrees of freedom within groups. Subtract 1 from the total number of subjects (values) to find total degrees of freedom.