1model,estimate,se,ci_low,ci_high2M1 unadjusted: growth ~ hours,-0.13169790632300882,0.014619618827634278,-0.1603518326928757,-0.103043979953141953M2 adjusted (main): growth ~ hours + skill_index,0.25353820594501253,0.009812212326345536,0.2343066231767153,0.272769788713309764R1 adds skill_index^2,0.25383792381516485,0.009844473118691516,0.23454311105575676,0.273132736574572935R2 adds hours x skill_index (effect at skill_index=0),0.2535986940513955,0.009917283395566277,0.23416117577160853,0.27303621233118256"S1 unadjusted, all 1200 rows incl. negative hours",-0.13518960504279864,0.013896968221774055,-0.16242716225177342,-0.107952047833823877"S2 adjusted, all 1200 rows incl. negative hours",0.25222449623309495,0.00947885217664965,0.23364628735208254,0.270802705114107378