The paper presents the application possibility of “Effect size” and Cohen’s-d index in the case of introduction of new milk products on the market. The field and online survey were used to establish the potential interest of final consumers for new functional food product of dairy company in Slovenia - milk with phytosterols additives. Two techniques possibilities of Cohen-d index were calculated; manual and using the Cohen’s-d calculator. Further, the application is focused on two main questions in survey regarding observed problem: 1) Would you buy milk with phytosterols additives, which scientifically proven lowers concentration of cholesterol in blood? 2) Would you pay for it at a higher price? The sample includes 419 surveys, 150 surveys were conducted on field (control group) and 269 surveys were provided online (experimental group). The Cohen’s-d index (d) results show by using manual and Cohen’s-d calculator for both groups “small” effect (d=0.35, i.e. d=0.34 ), and “zero or near zero” effect (d=0.15, i.e.= 0.15) when deciding to buy new milk product.U ovom radu prikazan je primjer mogućosti primjene “Utjecaja veličine” i Cohen-d indeksa u slučaju plasiranja novog mliječnog proizvoda na tržište. Terenska i online anketa korištene su za ocjenjivanje potencijalnog interesa potrošača za kupnju novog, funkcionalnog mliječnog proizvoda u Sloveniji - mlijeko s aditivom fitosterolom. Korišten je izračun za dvije vrste Cohen-d indeksa, ručno i pomoću Cohen’s-d kalkulatora na primjeru dvaju glavnih pitanja: 1) Zainteresirani ste za kupnju mlijeka s aditivom fitosterola, koji znanstveno dokazuje sniženje koncentracije kolesterola u krvi i 2) Spremni ste platiti za taj proizvod veću cijenu? Uzorak obuhvaća 419 anketa, od toga provedeno je 150 anketa na terenu (kontrolna skupina), dok je 269 anketa provedeno online (eksperimentalna skupina). Cohen-d indeks (d) rezultati prikazani su za dva prije spomenuta načina izračuna, “mali” učinak (d=0,35, odnosno d=0,34) i “nula ili blizu nule” učinak (d=0,15, odnosno = 0,15)
