Table 2.

Knowledge Items, Domains, and Item Characteristics for the Lung Cancer Screening Knowledge Measure.

Item	Domain	Item difficultyb	Item uncertaintyc	Index of discriminationd	Item-total correlatione	α if item deletedf	Test-retest reliabilityg
1.What percentage of lung cancer deaths are caused by smoking?	Attributable risk, smoking	20.8%	50.8%	23.4%	0.12	0.70	0.29
2.Is smoking the leading cause of lung cancer?a	Risk factors, smoking	84.2%	10.8%	40.0%	0.23	0.69	0.33
3.The most important thing smokers can do to lower their risk of lung cancer is to…a	Risk reduction, smoking	88.3%	2.5%	7.4%	-0.01	0.71	0.13
4.Where does lung cancer rank as a cause of cancer death in the US?	Risk, cause of death	25.8%	45.0%	53.1%	0.30	0.68	0.41
5.When should someone stop being screened for lung cancer? (Check all that apply)	Screening eligibility	47.5%	41.7%	52.6%	0.25	0.69	0.44
6.Should all current and former smokers be screened for lung cancer?a	Screening eligibility	2.5%	5.8%	2.9%	0.10	0.69	0.66
7.How many people with an abnormal CT scan will have lung cancer?	Predictive value of screening	2.5%	66.7%	2.9%	0.07	0.70	0.38
8.Does an abnormal CT scan mean a person has lung cancer?a	Predictive value of screening	63.3%	35.0%	75.4%	0.49	0.65	0.41
9.Can a CT scan suggest that you have lung cancer when you do not?	Screening accuracy, false positives	37.5%	50.8%	67.4%	0.40	0.66	0.36
10.Can a CT scan miss a tumor in your lungs?	Screening accuracy, false negatives	52.5%	37.5%	68.0%	0.38	0.67	0.49
11.Will all tumors found in the lungs grow to be life threatening?	Natural history, “over-diagnosis”	57.5%	30.0%	83.4%	0.52	0.65	0.45
12.Without screening, is lung cancer often found at a later stage when cure is less likely?	Screening benefit, mortality	72.5%	24.2%	52.6%	0.32	0.68	0.22
13.How much does screening for lung cancer with a CT scan lower your chances of dying from lung cancer?	Screening benefit, mortality reduction	1.7%	59.2%	-1.1%	0.00	0.70	0.20
14.Can a CT scan find lung disease that is not cancer?	Screening, secondary findings	70.0%	29.2%	77.1%	0.52	0.65	0.57
15.Can a CT scan find heart disease?	Screening, secondary findings	44.2%	50.0%	64.0%	0.29	0.68	0.28
16.Is radiation exposure one of the harms of lung cancer screening?	Screening risks	29.2%	42.5%	56.0%	0.33	0.67	0.39

Bolded items were included in the final lung cancer screening knowledge measure.

Abbreviations: CT = Computed tomography, α = alpha. All data were collected from 12/2014 to 09/2015 in Houston, TX.

^aItems were dropped from final lung cancer screening knowledge measure.

^bItem difficulty is the percentage correct responses.

^cItem uncertainty is the percentage of “I don't know” responses.

^dThe index of discrimination is the difference between percentage of respondents with correct responses for an item among those who scored in the upper versus lower quartiles of correct responses to the full scale. Items with an index of discrimination greater than 40% are considered acceptable for discrimination, and those with an index less than 20% are considered inadequate.

^eItem-Total Correlation is the correlation between the response on an individual question and the overall score on the survey.

^fα if item deleted represents the internal consistency of the scale without that item.

^gKappa coefficients are reported for baseline and 1-month, and represent average intercorrelation of items with dichotomous responses.