Reviewer ’s report  
 
Title: Correlates of use of withdrawal for contraception among women in Vietnam  
 
Version: 0 Date: 31 Dec 2019  
 
Reviewer: Summer L. Martins  
 
Reviewer's report:  
 
Thank you for the opportunity to review this manuscript, which addresses an important topic of 
public health significance. Withdrawal  is a complex behavior, used for both primary pregnancy 
prevention and as back -up for other methods. The nuances of withdrawal use are important to 
study given its low effectiveness in r elation to other methods. Overall, this is a well written 
paper. The Background is particularly strong re: methodological challenges and limitations 
related to studying withdrawal. The Discussion is also comprehensive in its review of limitations 
and impli cations.  
 
Exploratory studies are valuable and appropriate for understudied topics. However, this study has 
some important weaknesses. Some are inherent to the study design, but others can be overcome 
with some tweaks to the framing and analytic approach:  
 
1 -- The exploratory nature of the study is mentioned in Methods, but needs to be emphasized 
more strongly throughout the manuscript (title, abstract, background, discussion).    
 
2 --  The sample is quite homogeneous with respect to ethnicity, urbanicity,  and especially 
marital status. Ethnicity is mentioned in limitations, but urbanicity should also be addressed. 
Also, the characteristics of the sample (married, mean age 35, higher income, higher education) 
are not aligned with the populations at highest risk of unintended pregnancy. The relevance of 
the study to this important public health outcome is therefore limited. This needs to be addressed 
in the Discussion.  
 
3 -- The sample's homogeneity also has statistical implications. One needs some variation in 
measures to perform meaningful analyses. With 96.5% of the sample being married, 
comparisons by marital status should not be performed. Small cell sizes are furthe r compounded 
by the use of multinomial regression which, while appropriate for the outcome variable, result in 
data being spread across multiple outcome categories. I recommend the following:  
 
- Delete unmarried women from the analysis.  
 
- Delete women usin g infrequently reported methods (implant, sterilization, injectables, foam). 
This fosters a much simpler interpretation -- IUD or COC, less effective method 
(condom/rhythm) only, withdrawal alone or with less effective method.  
 
- Both of the restrictions ab ove can be detailed in Methods -- i.e. number and % of n=500 
excluded for these reasons.  
- Delete the multinomial regression, which is of limited value given sample size issues and lack 
of rationale for mutual adjustment of covariates. Focus instead on biv ariate analyses in Table 2, 
where prevalence ratios (with 95% CIs) could be added if relative measures are desired. Of note, 
2x2 calculations suggest that crude and adjusted ORs are roughly identical for withdrawal vs. tier 
1/2. 
 
     
 
 
Additional minor comme nts for each section are below.   
 
ABSTRACT  
 
1 -- Modify to reflect edits made based on this review.  
 
 
BACKGROUND  
 
2 -- P3, Line 42: Add citation for use of withdrawal as compensation for poor pill compliance.  
 
3 -- P3, Line 46: Rather than "erroneously" (wh ich struck me as judgmental), can you describe 
this more as using withdrawal due to misconceptions of the method as an effective STI/HIV 
prevention strategy?  
 
4 -- P3, Line 60: Add failure rate for another method such as the pill. Having a reference will 
help the reader understand just how less effective withdrawal is as a contraceptive method.  
 
5 -- P4, Lines 7 -9: This claim is debated and the consensus seems to be that while sperm is 
present, the clinical significance (for risk of pregnancy) is minimal, o r at least unclear. Please 
modify to represent the uncertainty in the literature.   
 
6 -- P4, Lines 22 -24: Use quotations around "naturalness." Also add citation for religious/cultural 
beliefs.  
 
7 -- P4, Lines 24 -29: Is reduced sensation reported by men, wo men, or both? Same for increased 
pleasure.  
 
8 -- P4, Line 33: Describe concerns in terms of population frequency rather than "strong." Also 
include prevalence/% for these concerns in the Vietnamese population.  
 
9 -- P4, Lines 35 -40: It's not clear at this point that the literature is sparse or what the gaps are --in 
general or for Vietnam. Either integrate this info in the previous paragraphs or add a couple of 
sentences here. This is a good opportunity to highlig ht gaps re: correlates of withdrawal use 
using more nuanced measures that account for exclusive vs. dual use.  
 
 
METHODS  
 
10 -- P4: Clarify sampling strategy. The abstract mentions stratified sampling, but that isn't 
mentioned here.  
 
11 -- P5, Lines 18 -20: M ore details are needed for survey topics and measures related to 
correlates. Under list of topics, add perceptions and beliefs as well as economic power in current 
relationship and importance of avoiding pregnancy. Briefly describe how these variables were  
measured -- phrasing, response scale -- and prepared for analysis. (It appears that Likert scales 
were used and then condensed for analysis?).  
 
12 -- P5, 38 -42: WHO categories is a good reference, but in your data only one method each 
from Tiers 1 and 2 (IUD and COC, respectively) are represented. Therefore it would be simpler 
to describe 3 categories: IUD or COC alone, less effective method (condoms/NFP) alone, or 
withdrawal.   
 
13 -- P5, Lines 47 -54: Add citations for some studies that informed your sele ction of covariates.  
 
14 -- P5, last paragraph: More info is needed here for your bivariate comparisons. What 
statistical tests were used? Was Fisher's exact test used for small cell sizes? Also modify this 
section if multinomial regression is dropped.  
 
 
RESULTS  
 
14 -- P6: Either here or in Methods, describe participation rate among those approached if this 
was collected.  
 
15 -- P6, Line 27: Was age normally distributed for all categories? If not, median would be more 
informative. Also include age categories  (e.g. 18 -24, 25 -34...) in Table 1 or narrative to give a 
better sense of the sample's age distribution.  
 
16 -- P6, Lines 38 -40: For whom is economic power not applicable? Unmarried women? If so, 
response categories can be changed to Yes/No if the analysis  is restricted to married women.  
 
17 -- For remainder of Results, edit as needed based on comments in this review.  
 
 
DISCUSSION  
 
18 -- P7, Line 38: Highlight additional limitations -- Frequency of use and adherence to methods 
(withdrawal and all others) wer e not measured.  
 
19 -- P8: Delete top paragraph, as use and barriers regarding Tier 1/2 methods is not the focus of 
this paper. The next paragraph is a very good summary of clinical implications.  
 
TABLES  
 
20 -- Table 1: Restrict to sample that was analyzed rather than all 500.  
 
21 -- Table 2: Modify to reflect changes to analysis.  
 
22 -- Table 3: Drop if multinomial analysis is deleted.  
 
Are the methods appropriate and well described?  
If not, please specify what is required in your comments to the authors.  
 
Yes 
 
Does the work include the necessary controls?  
If not, ple ase specify which controls are required in your comments to the authors.  
 
Unable to assess  
 
Are the conclusions drawn adequately supported by the data shown?  
If not, please explain in your comments to the authors.  
 
Yes 
 
Are you able to assess any statistics in  the manus cript or would you recommend an 
additional statistical review?  
If an additional statistical review is recommended, please speci fy what aspects require further 
assessment in your comments to the editors.  
 
I am able to assess the statistics  
 
Quality of written English  
Please indicate the quality of language in the manuscript:  
 
Acceptable  
 
Declaration of competing interests  
Please complete a declaration of competing interests, considering the following questions:  
 
1.  Have you in the past five years receiv ed reimbursements, f ees, funding, or salary 
from an organisation that may in any way gain or lose financial ly from the 
publication of this manuscript, either now or in the future?  
 
2.  Do you hold any stocks or shares in an organisation t hat may in any way gain or 
lose financially from the publication of this manuscript, either now or in the 
future?  
 
3.  Do you hold or are you currently applying for any patents relating to the content 
of the manuscript?  
 
4.  Have you received reimbursements, fees, funding, or salary from an organization 
that holds or has applied for patents relating to the content of the manuscript?  
 
5.  Do you have any other financial competing interests?  
 
6.  Do you have any  non-financial competing interests in relation to this paper?  
 
If you can answer no to all of the above, write 'I declare that I have no competing interests' 
below.  If your reply is yes to any, please give details below.  
 
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