The inclusion of a zero value in the range indicates that the variable being studied may have (17)____________.

The t test for two independent samples assumes that both underlying populations are (18)__________ and have (19)_________ variances. If sample sizes are (20) ________ and ________, violations of these assumptions will be of little concern.

The pooled variance estimate can be obtained by combining the variance common to both populations. The pooled variance estimate is the most accurate estimate of the variance (assumed to be the same for both populations) based on a combination of the two sample variances. The degrees of freedom for the pooled variance estimate equal the sum of the two sample sizes minus two. Two degrees of freedom are lost because the (21)________ in each of the two samples are expressed as (22)______ from their respective sample means.