Attic contracts more, Ionic less, than the other dialects. The laws of contraction often differ in the different dialects.
1. Ionic (Old and New) is distinguished by its absence of contraction. Thus, πλόος for πλοῦς
2. εο, εω, εου generally remain open in all dialects except Attic. In Ionic εω is usually monosyllabic. Ionic (and less often Doric) may contract εο, εου to ευ: σεῦ from σέο
3. αο, α_ο, αω, α_ω contract to α_ in Doric and Aeolic. Thus, Ἀτρείδα_ from Ἀτρείδα_ο, Dor. γελᾶντι
4. Doric contracts αε to η; αη to η; αει, αῃ to ῃ. Thus, νί_κη from νί_καε
5. The Severer (and earlier) Doric contracts εε to η, and οε, οο to ω. Thus, φιλήτω from φιλεέτω, δηλῶτε from δηλόετε, ἵππω from ἵππο-ο ( cross230 D.); the Milder (and later) Doric and N. W. Greek contract to ει, and ου. Aeolic agrees with the Severer Doric.
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].