Table 5. Differences of marginal means of difficulty indices across item-writing flaws.

IWF	Difficulty index (Flawed)	Difficulty index (Unflawed)	Difference in difficulty indices	Standard Error	Lower 95% confidence level	Upper 95% confidence level	P value
1	0.6132	0.5745	0.03869	0.1020	-0.1612	0.2386	0.7044
2	0.6623	0.6185	0.04379	0.1020	-0.1561	0.2437	0.6676
3	0.5038	0.5395	-0.03572	0.1020	-0.2356	0.1642	0.7262
4	0.4943	0.5178	-0.02349	0.1020	-0.2234	0.1764	0.8178
5	0.6073	0.5032	0.1041	0.1140	-0.1194	0.3276	0.3611
6	0.5815	0.6094	-0.02791	0.1020	-0.2278	0.1720	0.7844
7	0.5083	0.6396	-0.1313	0.1020	-0.3312	0.0684	0.1978
8	0.4720	0.4868	-0.01482	0.1020	-0.2147	0.1851	0.8845
9	0.7134	0.6302	0.08319	0.1020	-0.1167	0.2831	0.4147
10	0.5146	0.4698	0.04484	0.1020	-0.1550	0.2447	0.6602