Research: Adequate statistical power in clinical trials is associated with the combination of a male first author and a female last author
- University Medical Center Utrecht/Utrecht University, Netherlands
- VU University, Netherlands
- University Medical Center Utrecht/Utrecht University, The Netherlands
Figures
Figure 1
Percentage of adequately powered trials for the four different gender combinations of first and last author.
(A) Percentage of trials with power > 0.8 published between 1974 and 2017 for the four gender combinations (left panel) and for four periods (1975–1985; 1985–1995; 1995–2005; >2005) during this time (right panel). (B) Percentage of trials published with power > 0.7 (left) and power > 0.9 (right) for the four gender combinations. (C) Percentage of trials with power > 0.8 for the four gender combinations, including the trials were gender could not be determined for the first and/or last author (‘unknown’). Error bars represent the 95% confidence interval for proportions for all panels.
Figure 2
Percentage of adequately powered trials when the gender of the first and last author is male, female or unknown.
Left: Percentage of trials with power > 0.8 plotted for the gender of the first author (top) and the last author (bottom). Right: Percentage of trials with power > 0.8 plotted for four periods (1975–1985; 1985–1995; 1995–2005; >2005) for the gender of the first author (top) and the last author (bottom). Error bars represent the 95% confidence interval for proportions for all panels.
Figure 3
The proportion of included trials mapped per country on a white to red color scale (range: 0 – 24%).
The highest proportion of first authors were affiliated with an institution in the United States. Countries not present in any affiliation are plotted in gray.
Figure 4
The influence of geography on the percentage of trials that are adequately powered.
(A) Percentage of trials with power > 0.8 for the four gender combinations of first and last author within the three country groups. Error bars represent the 95% confidence interval for proportions. (B) A logistic regression multivariable model (see "Data analysis and statistical model" below) can be used to predict the probability that a trial will have a power above a certain value. Here the predicted probabilities that trials will have power > 0.8 are plotted as a function of year for the four gender combinations in the three country groups. The predicted probabilities are averaged across medical disciplines and plotted as mean and 95% confidence intervals.
Figure 5
Percentage of adequately powered trials, for the four gender combinations of the first and the last author, within 21 major medical disciplines.
Error bars represent the 95% confidence interval for proportions.
Figure 6
The percentage of the total number of trials underlying the four gender combinations within 21 major medical disciplines.
Error bars represent the 95% confidence interval for proportions.
Figure 7
The percentage of trials for the different gender combinations and periods studied.
Left: The number and percentage of trials underlying the power calculations for the four gender combinations. Right: The corresponding percentage of the total number of trials underlying the four gender combinations for the four periods studied (1975–1985; 1985–1995; 1995–2005; >2005). Error bars represent the 95% confidence interval for proportions for both panels.
Figure 8
Flow diagram of the 31,873 trials selected for analysis.
Trials were analyzed if published after 1974, included in a significant meta-analysis in a systematic review and gender data was extractable for both the first and the last author.
Tables
Table 1
Model estimates for the variables fitted against adequately powered trials.
https://doi.org/10.7554/eLife.34412.004| Variables | Odds ratio | 95% CI | Z value | P value | |
|---|---|---|---|---|---|
| Author combination | |||||
| Both females | 1.00 (ref.) | ||||
| Both males | 1.28 | 1.17 | 1.41 | 5.22 | <0.0001 |
| Female - male (last) | 1.25 | 1.13 | 1.39 | 4.29 | <0.0001 |
| Male - female (last) | 2.08 | 1.87 | 2.30 | 13.94 | <0.0001 |
| Time | |||||
| Publication year | 1.03 | 1.02 | 1.03 | 12.05 | <0.0001 |
| Country group | |||||
| Anglosphere | 1.00 (ref.) | ||||
| Europe | 0.76 | 0.71 | 0.81 | 8.87 | <0.0001 |
| Non-western | 0.87 | 0.80 | 0.94 | 3.69 | <0.0001 |
| Medical discipline | |||||
| Allergy & intolerance | 1.00 (ref) | ||||
| Blood disorders | 0.45 | 0.34 | 0.62 | 5.11 | <0.0001 |
| Child health | 0.47 | 0.36 | 0.61 | 5.68 | <0.0001 |
| Complementary medicine | 0.23 | 0.17 | 0.31 | 9.14 | <0.0001 |
| Consumer strategies | 0.66 | 0.41 | 1.03 | 1.80 | 0.072 |
| Dentistry & oral health | 1.05 | 0.68 | 1.59 | 0.21 | 0.832 |
| Developmental problems | 0.69 | 0.47 | 1.00 | 1.98 | 0.048 |
| Ear, nose & throat | 0.37 | 0.24 | 0.55 | 4.77 | <0.0001 |
| Effective health systems | 0.75 | 0.53 | 1.07 | 1.57 | 0.115 |
| Endocrine & metabolic | 0.29 | 0.20 | 0.42 | 6.51 | <0.0001 |
| Eyes & vision | 0.56 | 0.38 | 0.81 | 3.02 | 0.003 |
| Gastroenterology & hepatology | 0.49 | 0.38 | 0.65 | 5.07 | <0.0001 |
| Genetic disorders | 0.19 | 0.12 | 0.30 | 7.09 | <0.0001 |
| Gynaecology | 0.69 | 0.52 | 0.92 | 2.58 | 0.01 |
| Health & safety at work | 0.24 | 0.13 | 0.42 | 4.74 | <0.0001 |
| Heart & circulation | 0.29 | 0.22 | 0.39 | 8.24 | <0.0001 |
| Infectious disease | 0.61 | 0.47 | 0.80 | 3.62 | <0.0001 |
| Kidney disease | 0.80 | 0.58 | 1.12 | 1.28 | 0.201 |
| Lungs & airways | 0.35 | 0.27 | 0.46 | 7.56 | <0.0001 |
| Mental health | 0.53 | 0.40 | 0.71 | 4.40 | <0.0001 |
| Neonatal care | 0.47 | 0.34 | 0.64 | 4.68 | <0.0001 |
| Neurology | 0.56 | 0.42 | 0.74 | 4.08 | <0.0001 |
| Orthopaedics & trauma | 0.79 | 0.60 | 1.05 | 1.63 | 0.103 |
| Pain & anaesthesia | 0.64 | 0.49 | 0.84 | 3.23 | 0.001 |
| Pregnancy & childbirth | 0.58 | 0.44 | 0.77 | 3.76 | <0.0001 |
| Public health | 1.23 | 0.78 | 1.92 | 0.89 | 0.372 |
| Rheumatology | 0.75 | 0.57 | 1.00 | 2.02 | 0.043 |
| Skin disorders | 0.89 | 0.65 | 1.23 | 0.69 | 0.488 |
| Tobacco, drugs & alcohol | 0.34 | 0.26 | 0.46 | 7.39 | <0.0001 |
| Urology | 1.04 | 0.74 | 1.45 | 0.21 | 0.834 |
| Wounds | 0.36 | 0.21 | 0.61 | 3.73 | <0.0001 |
Table 2
Model estimates from the sensitivity analysis (with individual countries) for the variables fitted against adequately powered trials.
https://doi.org/10.7554/eLife.34412.005| Variables | Odds ratio | 95% CI | Z value | P value | |
|---|---|---|---|---|---|
| Author combination | |||||
| Both females | 1.00 (ref.) | ||||
| Both males | 1.25 | 1.13 | 1.37 | 4.58 | <0.001 |
| Female - male (last) | 1.19 | 1.07 | 1.32 | 3.28 | 0.001 |
| Male - female (last) | 1.98 | 1.78 | 2.19 | 12.95 | <0.001 |
| Time | |||||
| Publication year | 1.02 | 1.02 | 1.03 | 14.5 | <0.001 |
| Country | |||||
| Argentina | 1.00 (ref.) | ||||
| Australia | 0.79 | 0.52 | 1.19 | 1.12 | 0.261 |
| Austria | 1.31 | 0.84 | 2.02 | 1.19 | 0.232 |
| Bangladesh | 3.29 | 2.00 | 5.41 | 4.69 | <0.001 |
| Belgium | 0.94 | 0.61 | 1.45 | 0.29 | 0.775 |
| Brazil | 0.98 | 0.63 | 1.51 | 0.10 | 0.92 |
| Canada | 1.16 | 0.78 | 1.72 | 0.72 | 0.474 |
| Chile | 0.74 | 0.39 | 1.42 | 0.89 | 0.371 |
| China | 1.20 | 0.8 | 1.81 | 0.87 | 0.383 |
| Colombia | 1.95 | 1.17 | 3.26 | 2.55 | 0.011 |
| Costa Rica | 0.00 | 0.00 | Inf | 0.14 | 0.891 |
| Croatia | 0.47 | 0.22 | 1.03 | 1.88 | 0.06 |
| Czech Republic | 0.71 | 0.45 | 1.13 | 1.45 | 0.147 |
| Denmark | 1.24 | 0.82 | 1.87 | 1.03 | 0.303 |
| Egypt | 1.78 | 1.13 | 2.79 | 2.50 | 0.013 |
| Finland | 0.88 | 0.58 | 1.32 | 0.63 | 0.527 |
| France | 0.91 | 0.61 | 1.37 | 0.44 | 0.663 |
| Gambia | 1.05 | 0.56 | 1.99 | 0.16 | 0.87 |
| Germany | 0.90 | 0.6 | 1.34 | 0.53 | 0.593 |
| Ghana | 0.84 | 0.48 | 1.48 | 0.61 | 0.544 |
| Greece | 0.46 | 0.29 | 0.75 | 3.12 | 0.002 |
| Hong Kong | 1.37 | 0.89 | 2.11 | 1.44 | 0.15 |
| Hungary | 2.87 | 1.75 | 4.7 | 4.18 | <0.001 |
| India | 0.89 | 0.58 | 1.35 | 0.56 | 0.573 |
| Indonesia | 0.71 | 0.34 | 1.48 | 0.93 | 0.354 |
| Iran | 1.14 | 0.73 | 1.79 | 0.59 | 0.557 |
| Ireland | 0.80 | 0.49 | 1.32 | 0.87 | 0.387 |
| Israel | 0.80 | 0.51 | 1.26 | 0.98 | 0.328 |
| Italy | 1.03 | 0.69 | 1.53 | 0.15 | 0.881 |
| Japan | 0.35 | 0.22 | 0.53 | 4.83 | <0.001 |
| Jordan | 3.91 | 2.09 | 7.32 | 4.27 | <0.001 |
| Kenya | 0.42 | 0.18 | 1.00 | 1.97 | 0.049 |
| Korea | 1.56 | 1.02 | 2.39 | 2.07 | 0.038 |
| Lebanon | 1.36 | 0.75 | 2.46 | 1.01 | 0.311 |
| Malawi | 0.12 | 0.03 | 0.52 | 2.83 | 0.005 |
| Malaysia | 0.78 | 0.34 | 1.79 | 0.59 | 0.552 |
| Mali | 0.75 | 0.29 | 1.91 | 0.61 | 0.543 |
| Mexico | 1.07 | 0.62 | 1.85 | 0.25 | 0.8 |
| Netherlands | 0.71 | 0.47 | 1.07 | 1.62 | 0.106 |
| New Zealand | 1.28 | 0.76 | 2.14 | 0.94 | 0.349 |
| Nigeria | 1.32 | 0.70 | 2.48 | 0.87 | 0.386 |
| Norway | 0.89 | 0.56 | 1.41 | 0.49 | 0.624 |
| Pakistan | 0.93 | 0.48 | 1.83 | 0.20 | 0.844 |
| Papua New Guinea | 0.00 | 0.00 | Inf | 0.10 | 0.918 |
| Peru | 0.99 | 0.57 | 1.7 | 0.04 | 0.967 |
| Poland | 0.39 | 0.22 | 0.68 | 3.29 | 0.001 |
| Portugal | 3.17 | 1.84 | 5.45 | 4.17 | <0.001 |
| Qatar | 0.00 | 0.00 | Inf | 0.11 | 0.916 |
| Saudi Arabia | 0.54 | 0.30 | 0.98 | 2.02 | 0.043 |
| Singapore | 1.14 | 0.68 | 1.93 | 0.50 | 0.614 |
| Slovenia | 0.00 | 0.00 | Inf | 0.11 | 0.91 |
| South Africa | 1.24 | 0.79 | 1.96 | 0.93 | 0.355 |
| Spain | 1.08 | 0.71 | 1.62 | 0.35 | 0.73 |
| Sweden | 1.24 | 0.83 | 1.85 | 1.03 | 0.301 |
| Switzerland | 0.66 | 0.43 | 1.02 | 1.89 | 0.059 |
| Taiwan | 0.45 | 0.29 | 0.71 | 3.43 | 0.001 |
| Thailand | 1.53 | 0.99 | 2.37 | 1.93 | 0.053 |
| Turkey | 0.64 | 0.42 | 0.98 | 2.06 | 0.039 |
| Uganda | 1.27 | 0.56 | 2.88 | 0.58 | 0.56 |
| UK | 1.25 | 0.84 | 1.85 | 1.10 | 0.273 |
| USA | 1.42 | 0.96 | 2.10 | 1.78 | 0.076 |
| Venezuela | 5.25 | 3.22 | 8.54 | 6.67 | <0.001 |
| Vietnam | 0.00 | 0.00 | Inf | 0.12 | 0.907 |
| Zimbabwe | 1.93 | 0.90 | 4.12 | 1.70 | 0.089 |
| Other countries | 0.75 | 0.48 | 1.17 | 1.28 | 0.201 |
| Medical discipline | |||||
| Allergy & intolerance | 1.00 (ref.) | ||||
| Blood disorders | 0.49 | 0.39 | 0.63 | 5.79 | <0.001 |
| Child health | 0.55 | 0.45 | 0.67 | 5.87 | <0.001 |
| Complementary medicine | 0.26 | 0.20 | 0.33 | 11.21 | <0.001 |
| Consumer strategies | 0.94 | 0.66 | 1.34 | 0.35 | 0.73 |
| Dentistry & oral health | 1.43 | 1.07 | 1.92 | 2.41 | 0.016 |
| Developmental problems | 0.78 | 0.58 | 1.05 | 1.64 | 0.101 |
| Ear, nose & throat | 0.51 | 0.39 | 0.68 | 4.66 | <0.001 |
| Effective health systems | 0.85 | 0.63 | 1.14 | 1.11 | 0.269 |
| Endocrine & metabolic | 0.4 | 0.30 | 0.53 | 6.58 | <0.001 |
| Eyes & vision | 0.51 | 0.38 | 0.70 | 4.27 | <0.001 |
| Gastroenterology & hepatology | 0.56 | 0.46 | 0.69 | 5.41 | <0.001 |
| Genetic disorders | 0.29 | 0.20 | 0.42 | 6.51 | <0.001 |
| Gynaecology | 0.82 | 0.66 | 1.01 | 1.84 | 0.066 |
| Health & safety at work | 0.54 | 0.37 | 0.79 | 3.16 | 0.002 |
| Heart & circulation | 0.34 | 0.27 | 0.43 | 9.43 | <0.001 |
| Infectious disease | 0.8 | 0.65 | 0.99 | 2.09 | 0.036 |
| Kidney disease | 0.71 | 0.55 | 0.92 | 2.59 | 0.01 |
| Lungs & airways | 0.47 | 0.38 | 0.58 | 7.04 | <0.001 |
| Mental health | 0.6 | 0.48 | 0.75 | 4.58 | <0.001 |
| Neonatal care | 0.38 | 0.29 | 0.48 | 7.81 | <0.001 |
| Neurology | 0.7 | 0.57 | 0.87 | 3.26 | 0.001 |
| Orthopaedics & trauma | 1.18 | 0.96 | 1.46 | 1.56 | 0.12 |
| Pain & anaesthesia | 0.73 | 0.60 | 0.90 | 2.92 | 0.003 |
| Pregnancy & childbirth | 0.69 | 0.55 | 0.85 | 3.40 | 0.001 |
| Public health | 1.72 | 1.24 | 2.37 | 3.27 | 0.001 |
| Rheumatology | 0.97 | 0.78 | 1.20 | 0.31 | 0.757 |
| Skin disorders | 1.26 | 0.99 | 1.59 | 1.89 | 0.058 |
| Tobacco. drugs & alcohol | 0.4 | 0.32 | 0.50 | 7.97 | <0.001 |
| Urology | 1.27 | 1.00 | 1.63 | 1.92 | 0.054 |
| Wounds | 0.8 | 0.59 | 1.08 | 1.44 | 0.15 |
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Research: Adequate statistical power in clinical trials is associated with the combination of a male first author and a female last author
eLife 7:e34412.
https://doi.org/10.7554/eLife.34412
