def calculate_target_data(data):
    """
    Calculate the average value of a list of target data.

    Args:
        data (list): A list of tuples containing target data.

    Returns:
        tuple: The average value and its corresponding index.
    """
    if not data:
        return None
    
    total_value = sum(t[1] for t in data)
    avg_value = total_value / len(data)
    
    # Find the index of the data point with the highest value
    max_index = max(enumerate(data), key=lambda x: x[1][1])[0]
    
    return (avg_value, max_index)

# Example usage:
data = [('v5_1768236144', 108217.11959687909, 721, 15009.3),
        ('v5_1768235312', 89435.63603047856, 734, 12184.7),
        ('v5_1768235983', 98379.19963352643, 987, 9967.5)]

result = calculate_target_data(data)
print(result)