Types of studies

Randomised or quasi‐randomised controlled trials. We will impose no restrictions with regard to language or publication status. We will exclude cluster‐randomised studies. We will include cross‐over studies if data are available separately for the study period prior to cross‐over.

Types of participants

Adults with ED, irrespective of type and pathologic basis. Trials that included men with ED and with comorbid conditions such as cardiovascular disorder, spinal cord injury, prostate cancer and diabetes will be eligible (Khera and Goldstein 2011).

We will include trials in which only a subset of participants are eligible as long as data are available separately for the relevant subsets.

Types of interventions

All types of ginseng, regardless of species (e.g. Panax ginseng, Panax quinquefolius and Panax japonicus), processed status (e.g. white ginseng or red ginseng), or dose will be included.

We will include any trials comparing any type of ginseng to placebo, and PDE‐5 inhibitors. Trials in which ginseng forms part of a complex herbal medicine will be excluded. If the control groups are related to other types of herbal medicines and complementary therapies, we will exclude those studies.

We will include ginseng as the only treatment or with other 'conventional' treatments, as long as the same standard treatment is provided to both groups. 'Conventional' treatment interventions include phosphodiesterase inhibitors (e.g. sildenafil, tadalafil or vardenafil), injection (e.g. intracavernosal alprostadil), vacuum devices, or psychosexual counselling (Khera and Goldstein 2011).

Types of outcome measures

Measurement of outcomes assessed in this review will not be used as criteria for exclusion.

Electronic searches

We will search the following electronic databases.

• Cochrane Central Register of Controlled Trials (CENTRAL; latest issue) in the Cochrane Library; (for the search strategy, see Appendix 1).

• MEDLINE Proquest (from 1946; see Appendix 2).

• Embase Proquest (from 1947; see Appendix 3).

• CINAHL EBSCO (Cumulative Index to Nursing and Allied Health Literature; from 1981).

• AMED Proquest (Allied and Complementary Medicine Database; from 1985).

• Chinese Medical Database (China National Knowledge Infrastructure (CNKI); www.cnki.net/;from 1994).

• Wanfang Data Knowledge Service Platform (www.wanfangdata.com/; from 1982).

• Chinese Scientific and Technological Journals Database (VIP; www.cqvip.com/; from 1989).

• Japan Science and Technology Information Aggregator (J‐STAGE; www.jstage.jst.go.jp; from 1921).

• Korean Medicine Information System (Oriental Medicine Advanced Searching Integrated System (OASIS)/Korea Institute of Oriental Medicine; oasis.kiom.re.kr/eng/main.jsp; from 1963).

• KoreaMed (Korean Association of Medical Journal Edition; www.koreamed.org/; from 1958).

• Korean Medical Database (KMbase; Medical Research Information Center; kmbase.medric.or.kr/; from 1958).

• Research Information Service System (RISS; Korea Education & Research Information Service; www.riss.kr/; from 1958).

• The Town Society of Science Technology (TSSN; Korea Institute of Science andTechnology Information; society.kisti.re.kr/; from 1963).

• Korean Studies Information Service System (KISS; Korean Studies Information; kisseng.kstudy.com/; from 1954).

• Korean Traditional Knowledge Portal (KTKP; Korean Intellectual Property Office; www.koreantk.com/ktkp2014/?lang=en; from 1963).

We will search for ongoing studies by accessing the following databases.

• World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP; apps.who.int/trialsearch/).

• Chinese Clinical Trial Registry (http://www.chictr.org.cn/enIndex.aspx).

• International Standard Randomised Controlled Trial Number Register (ISRCTN; www.controlled‐trials.com/isrctn/).

• U.S. National Institutes of Health Clinical Trials Database (www.ClinicalTrials.gov).

• Clinical Research Information Service (CRIS) (cris.nih.go.kr/cris/en/search/basic_search.jsp) of the Republic of Korea.

In addition, we will search abstract proceedings of the annual meetings of the American Urological Association from 1996, European Association of Urology from 2004 and International Society of Sexual Medicine from 2004 for relevant records.

Searching other resources

The bibliographic references of all included trials will be reviewed to identify other potentially relevant studies. We will also manually search relevant journals, such as Journal of Ginseng Research (from 1976) (,http://ocean.kisti.re.kr/IS_mvpopo001P.do?method=multEMain&poid=skg&sFree= or http://www.ginsengres.org/). If available, we will also review unpublished conference proceedings (e.g. Proceedings of the Ginseng Society Conference (from 1974) and the Korean Oriental Medical Society Conference (from 1963)) and internal reports relevant to ginseng and erectile dysfunction. We will contact the authors of the included studies and researchers in the field with regard to any potential ongoing and unpublished studies, if necessary. We will also contact the main manufacturers of ginseng products to identify unpublished and relevant trials.

Selection of studies

We will use reference management software to remove duplicates at the beginning of the selection process. Two review authors (Lee HW, Kim T‐H) will independently scan the abstract, title, or both, of remaining records retrieved, to determine which studies should be assessed further. Two review authors (Lee HW, Kim T‐H) will investigate the full text of all potentially relevant records, map records to studies, and classify studies as included studies, excluded studies, studies awaiting classification, or ongoing studies in accordance with the criteria for each provided in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011a). We will resolve any discrepancies through consensus or recourse to a third review author (Lee MS). If resolution of a disagreement is not possible, we will designate the study as 'awaiting classification' and we will contact study authors for clarification. We will document reasons for exclusion of studies that may have reasonably been expected to be included in the review in a 'Characteristics of excluded studies' table. We will present an adapted PRISMA flow diagram showing the process of study selection (Liberati 2009).

Data extraction and management

Three review authors (Lee HW, Lee MS, Kim T‐H) will independently extract data from the reports of included studies using a data collection form that we will pilot test ahead of time on at least one study. We will resolve any disagreement by discussion or, where necessary, by arbitration by a fourth review author (Alraek T). The following study characteristics will be extracted and will be provided in the 'Characteristics of included studies' table.

• Methods: study design, duration of the study, the date when the study was conducted, trial setting, ethical approval.

• Participants: inclusion and exclusion criteria, age, country, ethnic group, total number of participants enrolled and numbers of participants randomised to the ginseng and control groups, causes of erectile dysfunction, severity of erectile dysfunction, the number of drop‐out participants.

• Interventions: details of ginseng (route, frequency, duration as applicable, type and dose of whole extraction of ginseng, dose of active compound in ginseng or combination treatments), control interventions.

• Outcomes: the details of outcome definition, method of outcome measurement, timing of outcome measurement, and any relevant subgroups measured for each outcome.

• Others: study funding sources and the details of declarations of interest among the trialists.

We will extract outcomes data relevant to this Cochrane Review as needed for calculation of summary statistics and measures of variance. For dichotomous outcomes, we will attempt to obtain numbers of events and totals for population of a 2 × 2 table, as well as summary statistics with corresponding measures of variance. For continuous outcomes, we will attempt to obtain means and standard deviations or data necessary to calculate this information. We will provide information, including trial identifier, about potentially relevant ongoing studies in the table 'Characteristics of ongoing studies'. We will attempt to contact the corresponding authors of the included trial reports to obtain any key missing data. We will use the PROGRESS framework to assess ginseng for health equity including disadvantaged or low‐ and middle‐income country populations via the extraction of sociodemographic data of participants (O'Neill 2014).

Assessment of risk of bias in included studies

According to the guidelines of the Cochrane Handbook for Systematic Reviews of Interventions, we will assess risk of bias using the Cochrane's 'Risk of bias' assessment tool (Higgins 2011b). We will evaluate the following domains.

• Random sequence generation.

• Allocation concealment.

• Blinding of participants and personnel.

• Blinding of outcome assessment.

• Incomplete outcome data.

• Selective reporting.

• Other sources of bias.

We will judge risk of bias domains as 'low', 'high' or 'unclear' risk of bias, according to the criteria. We will present a 'Risk of bias' summary figure to illustrate these findings.

For performance bias (blinding of participants and personnel) and detection bias (blinding of outcome assessment), we will assess risk of bias on an outcome‐specific basis, and we will group outcomes according to whether measured subjectively or objectively when reporting our findings in the 'Risk of bias' tables. All of our primary and secondary outcomes will be reported by participants or partners and therefore they will be considered as subjective outcomes in both performance and detection bias.

We will assess the domain of incomplete outcome data on an outcome‐specific basis, and we will group outcomes as short‐term or long‐term when reporting our findings in the 'Risk of bias' tables. We will summarise the risk of bias for each study by outcome, as well as across studies and domains for each outcome. Three review authors (Lee HW, Lee MS, Kim T‐H) will assess the risk of bias independently. They will resolve disagreements by discussion or, where necessary, by arbitration by a fourth review author (Alraek T).

Measures of treatment effect

For dichotomous data, we will present treatment effects as risk ratios (RRs) with 95% confidence intervals (CIs). For continuous data, we will express treatment effects as mean differences (MDs) with 95% CIs, unless different studies use different measures to assess the same outcome, in which case we will express data as standardised mean differences (SMDs) with 95% CIs. We will conduct all statistical analyses using Cochrane’s software program Review Manager 5 (RevMan).

Unit of analysis issues

If we identify cross‐over trials for inclusion, we will adopt the first phase of the study data for analysis. Data from multiple time‐point observations will be classified as short‐term (within four weeks) or long‐term (over four weeks) follow‐up. Should we identify trials with more than two intervention groups for inclusion in the review, we will handle these in accordance with guidance provided in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011c).

Dealing with missing data

We will request missing data from the original study investigators, whenever possible. If missing data, which cannot be provided by the original study authors, are detected, we will make the assumption that these outcomes are classified as treatment failures, and only the available data will be analysed. Where possible, we will perform a sensitivity analysis to test this assumption, and we will discuss the potential impact on the findings.

Assessment of heterogeneity

In the event of excessive heterogeneity unexplained by subgroup analyses, we will not report outcome results as the pooled effect estimate in a meta‐analysis but will provide a narrative description of the results of each study. We will use the I² statistic to assess the level of heterogeneity among the included studies. We will adopt a tiered percentage scale for assessment of heterogeneity (e.g. 0% to 40% might not be important; 30% to 60% may represent moderate heterogeneity; 50% to 90% may represent substantial heterogeneity; 75% to 100% may represent considerable heterogeneity) as outlined in the Cochrane Handbook for Systematic Reviews of Interventions (Deeks 2011). If heterogeneity is observed, we will attempt to determine possible reasons for it by performing subgroup analysis (Deeks 2011).

Assessment of reporting biases

We will attempt to obtain study protocols to assess for selective outcome reporting. To detect publication bias, funnel plots will be drawn using Egger's method if more than 10 studies are included in an individual analysis (Egger 1997). We will consider whether asymmetry indicates a possible reporting bias.

Data synthesis

We will conduct meta‐analyses using the random‐effects model and 95% CIs. We will interpret random‐effects meta‐analyses with due consideration of the whole distribution of effects. In addition, we will perform statistical analyses according to the statistical guidelines contained in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011a). For dichotomous data, we will use the Mantel‐Haenszel method. For continuous data, we will use the inverse‐variance method.

Subgroup analysis and investigation of heterogeneity

We expect the following characteristics to introduce clinical heterogeneity and, if data are available, we will conduct predefined subgroup analysis according to the:

• dose of ginseng (≦ 600 mg/day and > 600 mg/day);

• cause of ED;

• baseline ED severity.

We will use the test for subgroup differences in RevMan to compare subgroup analyses if there are sufficient studies.

Sensitivity analysis

Sensitivity analysis will principally be conducted as follows.

1. Low risk of bias (exclusion of studies judged high risk or unclear risk of bias).

2. The option of using missing data (using the 'last observation carried forward' method).