It changes dependin on progress. In general "low" mean, you hardly pass any checks. Very low mean: no point investment at all (3). "Med" means you pass most ez checks with item support and the stat matters practically in combat. "High" mean this stat is you main-attack rescource and pass any checks.
First chapter:
low: 3-4; med: 5-6; high: 8+
Second chapter:
very low: 3; low: 4-5; med: 6-8; high: 9-12; very high: 12+