How to determine normalized temperature given various temperature inputs?

Question

I need to use a normalized temperature value, to check if someone has an illness.

I have written a function that converts from Celsius to Fahrenheit, but need to write the same function using normalized temperatures.

public void hasFever(int temperature1, int temperature2, int temperature3, int temperature4, String bodylocation) throws ArithmeticException, InputMismatchException {
    final int noOfTimesTempTaken = 4;
    if(bodylocation == "ear") { //Determine if someone has fever if temperature was taken by the ear
        final double feverTemperature = 98.6;   
        double temperature1InFahrenheit = (temperature1 * 9/5) + 32;
        double temperature2InFahrenheit = (temperature2 * 9/5) + 32;
        double temperature3InFahrenheit = (temperature3 * 9/5) + 32;
        double temperature4InFahrenheit = (temperature4 * 9/5) + 32;
        double avgTemp = (temperature1InFahrenheit + temperature2InFahrenheit + temperature3InFahrenheit + temperature4InFahrenheit) / noOfTimesTempTaken;
        if(avgTemp >= feverTemperature) {
            System.out.println("This person has a fever because their temperature of " + avgTemp + " is greater than normal which is 98.6");
        } else {
            System.out.println("This person does not have a fever because their temperature of " + avgTemp + " is less than normal which is 98.6");
        }
    }
}

Answer 1

First of all, it should be noted that normalized temperature is not a term with a recognized / standard meaning that is applicable here. The term normalize is sometimes used to mean "adjusted to deal with measurement inaccuracies", but that's not what you seem to be trying to do here.

(It must be said that you have not successfully clarified what you mean by normalize, so we have to guess. This is my best guess, based on what you have said.)

I think you are looking for something like this:

double VALID_FAHRENHEIT_TEMP_THRESHOLD = 60.0;  // say

public double normalizeToFahrenheit(double temp) {
    if (temp >= VALID_FAHRENHEIT_TEMP_THRESHOLD) {
        return temp;
    } else {
        return temp * (9.0 / 5.0) + 32.0;
    }
}

But the problem is that this kind of "normalization" is scientifically and mathematically unsound. We are assuming that if a number is less than a particular value it must in degrees Centigrade rather than degrees Fahrenheit. But that isn't necessarily true. Both the Centigrade and Fahrenheit scales go down to very low values.

More practically, if someone has drowned in freezing water, it is possible for their body temperature in Fahrenheit may be way down ... possible close to freezing point. It may well be lower that our chosen threshold. If we assume that it "must be" Centigrade and convert it, we report an incorrect temperature.

A related problem is that a strange temperature value could be the result of the user miss-reading a thermometer, miss-hearing a measurement, or miss-typing a value; e.g. 11.3 instead of 101.3. Applying a normalization to mistaken input would lead to even more misleading results.

---

So given that this "normalization" methodology is not valid, what should you do instead?

My suggestion is for your app to report an anomaly to the user. For example, show them a dialog like this:

  The temperature xy degrees is outside of the expected range for human 
  temperatures in Fahrenheit.  

  Options: 

     1) Accept as a Fahrenheit value.  
     2) Apply Centigrade to Fahrenheit conversion. 
     3) Switch device to Centigrade mode.  
     4) Reenter value.

Answer 2

I hope I understand your problem correctly. So you want to pass a universal temperature unit in to your function.

class Temperature {
    private final static double CELSIUS_OFFSET = 273,15;
    private final static double FAHRENHEIT_OFFSET = 32;
    private final static double FAHRENHEIT_FACTOR = 9.0 / 5.0;
    private final double tempInKelvin;

    private Temperature() {
        //Private constructor, so only this class can access it
    }

    public static Temperature fromKelvin(double tempInKelvin) {
        final Temperature temperature = new Temperature();
        temperature.tempInKelvin = tempInKelvin;
        return temperature;
    }

    public static Temperature fromCelsius(double tempInCelsius) {
        return fromKelvin(tempInCelsius - CELSIUS_OFFSET);
    }

    public static Temperature fromFahrenheit(double tempInFahrenheit) {
        return fromCelsius((tempInFahrenheit - FAHRENHEIT_OFFSET) / FAHRENHEIT_FACTOR);
    }

    public double getInKelvin() {
        return tempInKelvin;
    }

    public double getInCelsius() {
        return tempInKelvin + CELSIUS_OFFSET;
    }

    public double getInFahrenheit() {
        return getInCelsius()*FAHRENHEIT_FACTOR + FAHRENHEIT_OFFSET;
    }
}

Using this class you can do this:

//Example use (has to be in a method, of course):
final Temperature temp1 = Temperature.fromCelsius(39.2);
final Temperature temp2 = Temperature.fromFahrenheit(95.3);
final Temperature temp3 = Temperature.fromCelsius(39.1);
final Temperature temp4 = Temperature.fromCelsius(39.3);
hasFever(temp1, temp2, temp3, temp4, "ear");

//New hasFever() method:
public void hasFever(Temperature temp1, Temperature temp2, Temperature temp3, Temperature temp4, String bodylocation) {
    final int noOfTimesTempTaken = 4;
    //USE String.equals()!!!
    if(bodylocation.equals("ear")) { //Determine if someone has fever if temperature was taken by the ear
        final double feverTemperature = 98.6;
        double avgTemp = (temp1.getInFahrenheit() + temp2.getInFahrenheit() + temp3.getInFahrenheit() + temp4.getInFahrenheit()) / noOfTimesTempTaken;
        if(avgTemp >= feverTemperature) {
            System.out.println("This person has a fever because their temperature of " + avgTemp + " is greater than normal which is 98.6");
        } else {
            System.out.println("This person does not have a fever because their temperature of " + avgTemp + " is less than normal which is 98.6");
        }
    }
}

Now you have a universal Temperature class which basically has no accessable unit, until you specify which one you want. This also converts all units for you.