### Database Schema:
CREATE TABLE country (
	id	INTEGER	NOT NULL	PRIMARY KEY,
	country_name	TEXT	NULL	DEFAULT NULL
);

CREATE TABLE ranking_criteria (
	id	INTEGER	NOT NULL	PRIMARY KEY,
	ranking_system_id	INTEGER	NULL	DEFAULT NULL,
	criteria_name	TEXT	NULL	DEFAULT NULL,
	foreign key (ranking_system_id) references ranking_system (id)
);

CREATE TABLE university (
	id	INTEGER	NOT NULL	PRIMARY KEY,
	country_id	INTEGER	NULL	DEFAULT NULL,
	university_name	TEXT	NULL	DEFAULT NULL,
	foreign key (country_id) references country (id)
);

CREATE TABLE university_ranking_year (
	university_id	INTEGER	NULL	DEFAULT NULL,
	ranking_criteria_id	INTEGER	NULL	DEFAULT NULL,
	year	INTEGER	NULL	DEFAULT NULL,
	score	INTEGER	NULL	DEFAULT NULL,
	foreign key (university_id) references university (id),
	foreign key (ranking_criteria_id) references ranking_criteria (id)
);

CREATE TABLE university_year (
	university_id	INTEGER	NULL	DEFAULT NULL,
	year	INTEGER	NULL	DEFAULT NULL,
	num_students	INTEGER	NULL	DEFAULT NULL,
	student_staff_ratio	REAL	NULL	DEFAULT NULL,
	pct_international_students	INTEGER	NULL	DEFAULT NULL,
	pct_female_students	INTEGER	NULL	DEFAULT NULL,
	foreign key (university_id) references university (id)
);

CREATE TABLE ranking_system (
	id	INTEGER	NOT NULL	PRIMARY KEY,
	system_name	TEXT	NULL	DEFAULT NULL
);

### User's Query:
Among the universities in United States of America, what is the percentage of female students in year 2016?

### Extra Knowledge:
female students refers to DIVIDE(MULTIPLY(num_students, pct_female_students), 100); in United States of America refers to country_name = 'United States of America'; percentage refers to DIVIDE(SUM(DIVIDE(MULTIPLY(num_students, pct_female_students), 100)), SUM(num_students))
SELECT SUM(CAST(T2.pct_female_students * T2.num_students AS REAL) / 100) * 100 / SUM(T2.num_students) FROM university AS T1 INNER JOIN university_year AS T2 ON T1.id = T2.university_id INNER JOIN country AS T3 ON T3.id = T1.country_id WHERE T3.country_name = 'United States of America' AND T2.year = 2016