Table 2. Criteria for Study Quality Assessment

Table 2. Criteria for study quality assessment

1. Level of evidence based on study design

Level 1: Randomized clinical trial (RCT) or Quasi-RCT

Level 2: Non-randomized parallel group trial, before-and-after trial (prospective experimental study of different techniques conducted over different time periods), and prospective cohort study

Level 3: Case-control study, retrospective cohort study, and retrospective case series with historical or concurrent controls

2. Power[*] is adequate if the estimate to detect a 2.5% reduction in the failure risk and/or the risk of a single complication (hematoma, infection, etc) between study groups if control frequency is 3.5% (versus 1%) with alpha 0.05, bilateral, is 0.8 or more

3. Comparability of study groups is adequate if answer is Yes to 4 or more of the following criteria (two ± = one Yes, ? = No):

Comparability of study participants:

Yes: Multiple data showing comparability or comparability mentioned

±: Few data showing comparability

No: Any data showing non comparability

?: No data available to assess comparability of participants

Comparability of study periods:

Yes: Same periods

No: Different periods

?: No period specified

Comparability of settings:

Yes: Same setting

No: Different setting

?: No setting specified

Comparability of providers:

Yes: Same provider

No: Different provider

?: No provider specified

Comparability of follow-up methodology:

Yes: Same methods and same length of follow-up during full study

±: Same method and same length of follow-up during part of study

No: Different methods or length of follow-up

?: No methods or length of follow-up specified

Comparability of sample size of compared groups (ratio = sample size in experimental/exposed group: sample size in control group)

Yes: ratio > 4:6

±: ratio between 4:6 and 3:7

No: ratio < 3:7

?: No sample size specified

Comparability of compliance/follow-up rate between experimental/exposed and exposed groups

Yes: absolute difference between groups 10% or less

±: absolute difference between groups 11% to 20%

No: absolute difference between groups > 20%

?: no compliance/follow-up rate specified

4. Validity of effectiveness assessment is adequate if two or more of the following criteria are fulfilled:

1) Explicit criteria of failure in terms of number and motility of sperm and/or pregnancy;

 2) Explicit criteria of failure in terms of time after vasectomy;

3) Semen analysis systematically required in all men at a specified time after vasectomy.

5. Validity of complications assessment is adequate if two or more of the following criteria are fulfilled:

1) Explicit criteria of complications;

2) Blinded assessment;

3) Systematic assessment performed at a specified time after vasectomy.

6. Total compliance/follow-up rate are adequate if 80% or more.

7. Global assessment of study quality

Very high: Level 1 and all criteria (power, comparability of study groups, validity of effectiveness assessment, validity of complication assessment, and compliance/follow-up rate) assessed as adequate.

High: Level 2 and all, or Level 1 or 2 and most of the criteria assessed as adequate.

Moderate: Level 3 and most, or level 1 or level 2 and some of the criteria assessed as adequate.

Low: Level 3 and some, or level 1 or level 2 and almost none of the criteria assessed as adequate.

Very low: Level 3 and almost none, or any level andnone of the criteria assessed as adequate.

[*]Power (3.5% versus 1%); Binomial 2 sample arcsine power calculation done with UCLA Department of statistics software available at: