The effect size, study design, and development experience in commercially sponsored studies for new drug applications in approved drugs

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Table 1 Summary statistics of explanatory variables and effect sizes

Variable			n	%
Total number of test drug-comparator pairs observed			194	100
Endpoint	HDRS		19	10
	PANSS		12	6
	PEF		16	8
	Blood pressure		41	21
	HbA1c		24	12
	CGI-I	Depression	33	17
		Schizophrenia	25	13
		Asthma	24	12
Comparator	Placebo		44	23
Comparator	Active		150	77
Statistical purpose	Superiority		32	17
	Non-inferiority and equivalence		57	29
	Dose response		20	10
	Other		85	44
Number of arms	2		142	73
	3		28	14
	4		22	11
	5		2	1
	All		194	2.40 (0.729)^a
Sample size			194	236 (108)^a
Length of trial (weeks)			194	8.54 (4.10)^a
Mean number of subjects per site			182	5.14 (3.20)^a
Approval year			194	1999^b
Dosing schedule	Flexible		109	56
Dosing schedule	Fixed		85	44
Type of endpoint	Subjective endpoint (assessment score)		30	15
	Subjective endpoint		84	43
	(Clinical Global Improvement)
	Objective endpoint		80	41
Primary endpoint
	Yes		147	76
	No		47	24
Comparator with the same mode of action of the test drug
	Yes		153	79
	No		41	21
Phase2
	Yes		36	19
	No		158	81
Precedent foreign clinical trial data
	Yes		83	43
	No		111	57
Companies' domestic development experience with similar drugs
	Yes		91	47
	No		103	53
Mean age of subjects			193	48.0 (7.63)^a
Ratio of female subjects			194	0.47 (0.10)^a
Effect size	Placebo		44	0.58 (0.52)^a
Effect size	Active		150	0.08 (0.22)^a

^aMean (SD), ^bMedian.
Precedent foreign clinical data: a dummy variable that was assigned a value of 1 if foreign clinical trials were included in the clinical data package. Companies’ domestic development experience with similar drugs: a dummy variable that was assigned a value of 1 when a company had gained at least one drug approval for the same therapeutic indication in Japan before the approval of a drug we analyzed.
HDRS: the Hamilton Depression Rating Scale for depression, PNASS: Positive and Negative Syndrome Scale for schizophrenia, PEF: morning Peak Expiratory Flow for asthma, Blood pressure: diastolic pressure for hypertension, HbA1c: hemoglobin A1c for diabetes, CGI-I: Clinical Global Impression of Improvement.