“…Literature sources for each challenge. C1 QRs are neglected[6,10,12,17,20,21,[23][24][25][26][27][28][29]37,38,40,46,53,54,63,64,74-82] 30 C2 Minimal documentation [6,10,17,21,23,24,27,28,31-34,37,41,46,47,51,53-56,64,65,77,82] 25 C3 Inappropriate prioritisation method [10,20,21,23,25,27,30,34-37,39,40,46,47,54,59,60,62,74,77,83,84] 23 C4 Managing change [20,21,23,24,28,34,35,38-43,47,53,65,82-86] 21 C5 Poorly written requirements [20,21,27,28,34,37,38,40,44-47,54,55,59,61,71,74,78,87,88] 21 C6 Inaccurate effort estimation [10,20,21,23,24,27,31,40,43,46,48-54,62,89] 19 C7 Customer unavailable or low availability [10,20,21,23,24,27,28,34,38,40,47,53-55,59,65,74,77] 18 C8 Customer knowledge[21,23,24,31,38,46,47,[54][55][56]76,77,90] …”