Absolute change from baseline at week 24 was assessed as the average treatment effect at Week 16 and at Week 24. FEV1 is the volume of air that can forcibly be blown out in one second, after full inspiration. Hankinson and Wang standards were used to calculate percent predicted FEV1 (for age, gender, race, and height). The Hankinson standard was used for male participants 18 years and older and female participants 16 years and older. The Wang standard was used for male participants aged 12 to 17 years and for female participants aged 12 to 15 years.

Full Analysis Set (FAS) included all randomized participants who received any amount of study drug. Here, number of participants analyzed signifies participants who were evaluable for this outcome measure.

Assessed as the average treatment effect at Week 16 and at Week 24. FEV1 and percent predicted FEV1 are defined in Outcome Measure (OM) 1.

FAS. Here, number of participants analyzed signifies participants who were evaluable for this outcome measure.

BMI was defined as weight in kilogram (kg) divided by height*height in square meter (m^2).

FAS. Here, number of participants analyzed signifies participants who were evaluable for this outcome measure.

The CFQ-R is a validated participant-reported outcome measuring health-related quality of life for participants with cystic fibrosis. Respiratory domain assessed respiratory symptoms (for example, coughing, congestion, wheezing), the scaled score range: 0-100; higher scores indicating fewer symptoms and better health-related quality of life.

FAS. Here, number of participants analyzed signifies participants who were evaluable for this outcome measure.

A participant was considered as a responder if the participant had >=5% increase from baseline in average percent predicted FEV1 at Week 16 and at Week 24 (relative change). FEV1 and percent predicted FEV1 are defined in OM 1. A participant with a missing average relative change from baseline in percent predicted FEV1 at Week 16 and at Week 24 was considered as a non-responder.

FAS.

The total number of days on study is equal to the Week 24 date or the last dose date (whichever occurred last) minus the first dose date plus 1. The total number of years (48 weeks) on study is equal to the number of days on study divided by 336. Pulmonary exacerbation events per year (48 weeks) are reported.

FAS.

FAS. Here, number of participants analyzed signifies participants who were evaluable for this outcome measure.

Z-Score is a statistical measure to evaluate how a single data point compares to a standard. It describes whether a mean was above or below the standard and how unusual the measurement is with range from -infinity to +infinity; 0: same mean, >0: a greater mean, and <0: a lesser mean than the standard. BMI-for-age z-score was calculated by using centers for disease control and prevention (CDC) growth charts for the pediatric population.

FAS. Here, number of participants analyzed signifies participants who were evaluable for this outcome measure. Only participants who were <20 years of age were analyzed.

Time to first pulmonary exacerbation was assessed using Cox Regression method. For participants who completed 24 weeks of treatment, participants without a pulmonary exacerbation before treatment completion were considered censored at the time of treatment completion or at the Week 24 Visit (whichever occurred last). For participants who prematurely discontinued study treatment, participants without a pulmonary exacerbation through the Week 24 Visit were considered censored at the time of the Week 24 Visit.

FAS.

FAS.

EQ-5D-3L: participant rated questionnaire to assess health-related quality of life. It consists of EQ-5D descriptive system and EQ-5D Visual Analog Scale (VAS). EQ-5D-3L descriptive system comprises the following 5 dimensions: mobility, self-care, usual activities, pain/discomfort and anxiety/depression. Each dimension has 3 levels: no problems (1), some problems (2), and extreme problems (3). The 5 dimensional 3-level systems are converted into a single index utility score. Values for theoretically possible health states are calculated using a regression model and weighted according to the social preferences of the Unites States (US) general population. For this population, the possible EQ-5D-3L index scores ranges from -0.11 (that is, 3 for all 5 dimensions) to 1.0 (that is, 1 for all 5 dimensions), where higher scores indicate a better health state.

FAS. Here, number of participants analyzed signifies participants who were evaluable for this outcome measure.

The EQ-5D-3L VAS records the participant's self-rated health on a vertical, visual analogue scale where the best state a participant can imagine is marked 100 and the worst state a participant can imagine is marked 0, higher scores indicates a better health state.

FAS. Here, number of participants analyzed signifies participants who were evaluable for this outcome measure.

The TSQM is a 14-item self-administered questionnaire which measures participants' experiences with their medication on four dimensions: effectiveness, side effects, convenience and global satisfaction. For each dimension, responses are added and transformed to a scale from 0 to 100, where higher scores indicate greater satisfaction.

FAS. Here, "n" signifies participants who were evaluable for specified category for each arm, respectively.

AE: any untoward medical occurrence in a participant during the study; the event does not necessarily have a causal relationship with the treatment. This includes any newly occurring event or previous condition that has increased in severity or frequency after the informed consent form is signed. AE includes serious as well as Non-serious AEs. SAE (subset of AE): medical event or condition, which falls into any of the following categories, regardless of its relationship to the study drug: death, life threatening adverse experience, in-patient hospitalization/prolongation of hospitalization, persistent/significant disability or incapacity, congenital anomaly/birth defect, important medical event. Any AE that increased in severity or that was newly developed at or after the initial dosing of study drug to 28 days after the last dose of study drug is considered treatment-emergent.

Safety Set (SS) included all randomized participants who received any amount of study drug. Participants were analyzed as per actual treatment received.

Ctrough, Ctrough,avg, C3-6h, and C3-6h,avg for lumacaftor, M28 lumacaftor (lumacaftor metabolite), ivacaftor, M1 ivacaftor (ivacaftor metabolite), and M6 ivacaftor (ivacaftor metabolite) were calculated. C3-6h,avg is average of individual 3 to 6 hours post-dose observed concentrations across Day 15, and Weeks 4 and 8 and Ctrough,avg is average of individual pre-dose observed concentrations across Weeks 4, 8, and 16. This outcome was not planned to be assessed in Placebo arm.

Pharmacokinetic (PK) population included all randomized participants who received at least one dose of study drug and had a PK assessment. Here, number of participants analyzed signifies participants who were evaluable for this outcome measure and "n" signifies participants evaluable for specified category for each arm, respectively.