Figure 1 presents the typical stages in a simple RCT. The research design depicted has two treatment arms (A and B). Subjects are assessed immediately before (T0) and after treatment (T1), and also complete a second outcome assessment at a later point (T2).
There are four columns of text boxes. The steps in the research process used to organize this figure are listed in dashed boxes in the far left column. Solid boxes in the second and fourth columns refer to groups of (potential) subjects that we want to maximize; each box is labeled with N and numbered 1 through 11, and after step 7 (randomization) are identified either a. (Arm A) or b. (Arm B). Dotted boxes in the third column refer to groups of (potential) subjects that we want to minimize or avoid altogether; they are not in either treatment arm, so have no "N" label.
Column 1: Steps in the Research Process (far left column).
Column 2: Groups to Maximize (Pre-randomization and Arm A).
Column 3: Groups to Minimize.
Column 4: Groups to Maximize (Arm B) (far right, beginning with step 7. Randomization).
Arrows are used to show the relationship of the various boxes to the steps in the research process.
Recruitment has a right arrow pointing between N1. Population and N2. Interested (Groups to Maximize, Arm A).
N1. Population has an arrow leading down to N2. Interested and to the right, Not interested (Groups to Minimize).
Prescreening has a right arrow pointing between N2. Interested and N3. Probably eligible (Groups to Maximize, Arm A).
N2. Interested has an arrow leading down to N3. Probably eligible and to the right, Probably ineligible (Groups to Minimize).
Obtaining consent has a right arrow pointing between N3. Probably eligible and N4. Willing (Groups to Maximize, Arm A).
N3. Probably eligible has an arrow leading down to N4. Willing and to the right, Unwilling (Groups to Minimize).
Screening has a right arrow pointing between N4. Willing and N5. Eligible (Groups to Maximize, Arm A).
N4. Willing has an arrow leading down to N5. Eligible and to the right, Ineligible (Groups to Minimize).
Baseline assessment has a right arrow pointing between N5. Eligible and N6. Assessed cases T0.
N5. Eligible has an arrow leading down to N6. Assessed cases T0 (Groups to Maximize, Arm A) and to the right, Not assessed T0 (Groups to Minimize).
Randomization has a right arrow pointing between N6. Assessed cases T0 and N7a. Randomized Arm A (Groups to Maximize, Arm A).
N6. Assessed cases T0 has an arrow leading down to N7a. Randomized Arm A; to the right, Not randomized (Groups to Minimize); and to the far right, N7b. Randomized Arm B (Groups to Maximize, Arm B).
Treatment has a right arrow pointing between N7a. Randomized Arm A and N8a. Treated cases (Groups to Maximize, Arm A).
N7a. Randomized Arm A has an arrow leading down to N8a. Treated cases; to the right, Incompletely treated (Groups to Minimize).
N7b. Randomized Arm B has an arrow leading down to N8b. Treated cases (Groups to Maximize, Arm B); to the left, Incompletely treated (Groups to Minimize).
Incompletely treated also has arrows pointing to N9a. and N9b., Assessed cases T1 (Groups to Maximize, Arms A and B).
Outcome assessment has a right arrow pointing between N8a. Treated cases and N9a. Assessed cases T1 (Groups to Maximize, Arm A).
N8a. Treated cases has an arrow leading down to N9a. Assessed cases T1; to the right, Not assessed T1 (Groups to Minimize).
N8b. Treated cases has an arrow leading down to N9b. Assessed cases T1 (Groups to Maximize, Arm B); to the left, Not assessed T1 (Groups to Minimize);
Not assessed T1 also has arrows pointing to N10a. and N10b., Tracked cases (Groups to Maximize, Arms A and B).
Tracking cases has a right arrow pointing between N9a. Assessed cases T1 and N10a. Tracked cases (Groups to Maximize, Arm A).
N9a. Assessed cases T1 has an arrow leading down to N10a. Tracked cases; to the right, Lost to follow-up (Groups to Minimize).
N9b. Assessed cases T1 has an arrow leading down to N10b. Tracked cases (Groups to Maximize, Arm B); to the left, Lost to follow-up (Groups to Minimize).
Re-assessing outcomes has a right arrow pointing between N10a. Tracked cases and N11a. Assessed cases T2 (Groups to Maximize, Arm A).
N10a. Tracked cases has an arrow leading down to N11a. Assessed cases T2; to the right, Not assessed T2 (Groups to Minimize).
N10b. Tracked cases has an arrow leading down to N11b. Assessed cases T2 (Groups to Maximize, Arm B); to the left, Not assessed T2 (Groups to Minimize).
Data analysis has a right arrow pointing between N11a. Assessed cases T2 and a large box, Analyzed, that encompasses the area under all three right hand columns. Small arrows indicate that data from all three columns feed into the Analyzed box.