Comparisons can also look at tests of trend, such as linear and quadratic relationships, when the independent variable involves ordered levels.
kəmpˈæɹɪsənz kæn ˈɔːlsoʊ lˈʊk æt tˈɛsts ʌv tɹˈɛnd, sˈʌtʃ ɐz lˈɪnɪɹ ænd kwɑːdɹˈæɾɪk ɹᵻlˈeɪʃənʃˌɪps, wˌɛn ðɪ ˌɪndᵻpˈɛndənt vˈɛɹɪəbəl ɪnvˈɑːlvz ˈɔːɹdɚd lˈɛvəlz.