A web-based interview that includes open-ended questions regarding blood donation knowledge.

Attitudes toward blood donation will be assessed using a 6-item measure where individuals are asked to rate how donating blood in the next 8 weeks would seem using a 7-item Likert-type scale. The scale distinguishes between cognitive attitudes (evaluative judgments: useful versus useless, pointless versus worthwhile, the wrong thing to do versus the right thing to do) and affective attitudes (emotional reactions: unpleasant versus pleasant, unenjoyable versus enjoyable, frightening versus not frightening). Total scores on the scale range from 6 to 42, with higher scores reflecting more positive attitudes toward blood donation.

Individuals' perception of control over their ability to donate blood will be assessed using a 6-item measure that assesses two components of perceived behavioral control: self-efficacy (three items) and controllability (three items). Items on the self-efficacy sub-scale ask about how confident the participant is in their ability to donate blood in the next 8 weeks, while the controllability sub-scale assesses how much control participants feel they have over whether or not they donate blood. Participants are asked to rate each item on a 7-point Likert-type scale. Total scores on the scale range from 6 to 42, with higher scores reflecting greater perception of control over ones ability to donate blood.

Individuals' perception about subjective norms will be assessed using a six item, 7-point Likert-type scale, with anchors at 1 (disagree/unlikely) and 7 (agree/likely). Total scores on the scale range from 6 to 42. The measure assesses both descriptive norms (perceived behavior of others) and injunctive norms (what an individual believes others want from him/her).

Blood Donor Identity will be measured using an 18-item scale that examines an individual's motivation to donate on the six motivational factors proposed by Self Determination Theory: amotivation, external regulation, introjected regulation, identified regulation, integrated regulation, and intrinsic regulation. Participants are asked to rate their agreement with each item on a 7-point Likert-type scale, with individual item scores ranging from 1 (not at all true) to 7 (very true). A composite score for the total scale is calculated by combining the six subscale scores using the weighting of -3, -2, -1, +1, +2, +3 for the amotivation, external regulation, introjected regulation, identified regulation, integrated regulation, and intrinsic regulation subscales, respectively, in order to produce a single Relative Autonomy Index score.

Anxiety will be assessed using the Blood Donor Anxiety Scale, a six-item scale that assesses for both the presence (3 items) and absence (3 items) of anxiety. Participants rate their agreement on how relaxed, content, pleasant, tense, nervous and jittery they would feel if they donated blood on a 4-point scale, with anchors at 1 (not at all) and 4 (very much). Composite scores on the scale range from 3 to 12, with higher scores on the presence subscale reflecting more anxiety, and higher scores on the absence subscale reflecting less anxiety about a future donation.

The 6-item ambivalence scale asks participants to rate how true a statement is for them on a 7-point scale (1=Not at all true to 7=Very true). Separate subscale scores are calculated for commitment and indecision (scores ranging from 3 to 21 for each subscale).

To assess whether the Motivational Interview intervention supported the basic psychological needs of autonomy, competence, and relatedness, a 9-item Likert-type scale will be utilized (3 items per psychological need, anchors at 1 = Not at All and 7 = Extremely).

Participants will be asked a series of questions regarding their experience during the interview.