def getTotalInAge(nodeState, ageTest):
    """Get the size of the population within an age group.

    :param nodeState: The disease states of the population stratified by age.
    :type nodeState: A dictionary with a tuple of (age, state) as keys and the number of individuals
    in that state as values.
    :param ageTest: The age range of the population.
    :type ageTest: str, e.g. '70+'
    :return: The population size within the age range.
    :rtype: int
    """
    total = 0
    for (age, _), value in nodeState.items():
        if age == ageTest:
            total += value
    return total