τj = differential effect (response) associated with the j level of X;  this assumes that overall the values of τj add to zero (that is, )
tˈaʊdʒ ˈiːkwəlz dˌɪfɚɹˈɛnʃəl ɪfˈɛkt ɹᵻspˈɑːns ɐsˈoʊsɪˌeɪɾᵻd wɪððə dʒˈeɪ lˈɛvəl ʌv ˈɛks;  ðɪs ɐsˈuːmz ðæt ˌoʊvɚɹˈɔːl ðə vˈæljuːz ʌv tˈaʊdʒ ˈæd tə zˈiəɹoʊ ðæt ˈɪz,