TABLE 2

Performance of all items of the daily version of PROactive Physical Activity in COPD (chronic obstructive pulmonary disease) instrument (D-PPAC) and activity monitors during item reduction

	Item flagged due to						Selected item
	Floor/ceiling effect	Not fitting unidimensionality	Redundancy	Not proper order	Differential Item Functioning	Less important according to patients/experts
Factor 1 “Amount of physical activity”
Walking outside							x
Chores inside		x			x	x
Chores outside							x
Physical leisure		x		x
Intensity^#		x
Time in locomotion^#			x
Standing time^#		x			x	x
VMU·min⁻¹^#							x
Steps^#							x
MVPA^¶			x	x
VMU·min⁻¹^¶							x
Steps^¶							x
Factor 2 “Difficulty with physical activity”
Difficulty getting dressed							x
Difficulty carrying things	x	x				x
Difficulty climbing stairs	x	x		x		x
Difficulty showering	x			x		x
Difficulty taking a bath	x			x		x
Difficulty bending over	x	x			x
Difficulty washing yourself	x		x			x
Difficulty walking up a small slope	x	x				x
Difficulty when hurrying	x					x
Avoid activities							x
Breathless in general							x
Lack physical strength			x			x
Lack of strength in legs		x				x
Tired in general							x
Take breaks							x
Pace yourself			x			x
Prevented from doing activities	x		x
Breathless walking on level ground			x			x
Slow down while walking			x			x
Breathless climbing stairs		x				x
Time to recover			x			x
Spread activities	x			x
Stop doing activities	x		x	x
Puffs in addition	x	x				x
Consider lung problems when planning	x		x
Help from others	x	x	x	x		x

VMU: vector magnitude unit; MVPA: moderate-to-vigorous physical activity. ^#: data from Dynaport; ^¶: data from Actigraph.