Of key concern in any research are 1.) is there an effect 2.) what is the effect and 3.) what is the extent of the effect?   A method for considering points one and three is to calculate the effect size using a calculation called Cohen's d.   In my own doctoral research, Cohen's d was used to calculate the effect size of changes in teacher's Pedagogical Content Knowledge resulting from the use of 3D-PAST during NGSS-aligned professional development activities.   

The interactive shown below was developed by Kristopher Magnusson and is an excellent visualization of the meaning of effect size.