/// <summary>
/// Builds a dictionary key using a provided sex and measurement value.
/// </summary>
/// <param name="measurement">The measurement in metric units</param>
/// <param name="sex">Whether the child is male or female</param>
/// <returns>int; represents the integer dictionary key for the given sex and measurement values</returns>
internal int BuildKey(Sex sex, double measurement)
{
if (StatisticsHelper.IsWholeNumber(measurement))
{
int sexKeyPart = sex == Sex.Male ? 1 : 2;
int measurementKeyPart = (int)(measurement * 100) + sexKeyPart;
return(measurementKeyPart);
}
return(-1);
}
/// <summary>
/// Calculates a z-score for a given indicator, pair of measurements (measurement1-for-measurement2, as
/// in "BMI-for-Age"), and gender.
/// </summary>
/// <param name="indicator">The indicator to use for computing the z-score (e.g. BMI, Height-for-Age, Weight-for-Age, etc.)</param>
/// <param name="measurement1">
/// The first measurement value. Must be in metric units and must be greater than or equal to zero. For
/// example, if the indicator is 'Height-for-Age', then measurement1 represents the child's height in
/// centimeters. Note that subscapular skinfold and triceps skinfold require measurement1 be provided
/// in millimeters.
/// </param>
/// <param name="measurement2">
/// The second measurement. Typically age of the child in days. For example, if the indicator is
/// 'Height-for-Age', then measurement2 represents the child's age. If the indicator is instead
/// 'Weight-for-Length' or 'Weight-for-Height' then measurement2 represents the child's length or
/// height (respectively) and must be a non-zero value provided in centimeters. Automatically
/// rounded to 5 decimal values if measuring height or length and automatically rounded to a whole
/// number if measuring age in days.
/// </param>
/// <param name="sex">Whether the child is male or female</param>
/// <returns>double; the z-score for the given inputs</return>
internal double CalculateZScore(Indicator indicator, double measurement1, double measurement2, Sex sex)
{
if (measurement1 < 0)
{
throw new ArgumentOutOfRangeException(nameof(measurement1));
}
if (!IsValidMeasurement(indicator, measurement2))
{
throw new ArgumentOutOfRangeException(nameof(measurement2));
}
measurement2 = Math.Round(measurement2, 5);
Dictionary <int, Lookup> reference = null;
bool shouldRound = true;
switch (indicator)
{
case Indicator.BodyMassIndexForAge:
reference = WHO2006_BMI;
break;
case Indicator.WeightForLength:
reference = WHO2006_WeightForLength;
shouldRound = false;
break;
case Indicator.WeightForHeight:
reference = WHO2006_WeightForHeight;
shouldRound = false;
break;
case Indicator.WeightForAge:
reference = WHO2006_WeightForAge;
break;
case Indicator.ArmCircumferenceForAge:
reference = WHO2006_ArmCircumference;
break;
case Indicator.HeadCircumferenceForAge:
reference = WHO2006_HeadCircumference;
break;
case Indicator.HeightForAge:
case Indicator.LengthForAge:
reference = WHO2006_LengthHeightForAge;
break;
case Indicator.SubscapularSkinfoldForAge:
reference = WHO2006_SubscapularSkinfoldForAge;
break;
case Indicator.TricepsSkinfoldForAge:
reference = WHO2006_TricepsSkinfoldForAge;
break;
default:
throw new ArgumentOutOfRangeException(nameof(indicator));
}
if (shouldRound && !StatisticsHelper.IsWholeNumber(measurement2))
{
measurement2 = Math.Round(measurement2, 0);
}
int key = BuildKey(sex, measurement2);
Lookup lookup = null;
bool found = reference.TryGetValue(key, out lookup);
if (found)
{
return(StatisticsHelper.CalculateZScore(measurement1, lookup.L, lookup.M, lookup.S, true));
}
else if (indicator == Indicator.WeightForLength || indicator == Indicator.WeightForHeight)
{
var interpolatedLMS = InterpolateLMS(sex, measurement2, reference);
return(StatisticsHelper.CalculateZScore(measurement1, interpolatedLMS.Item1, interpolatedLMS.Item2, interpolatedLMS.Item3, true));
}
else
{
throw new InvalidOperationException($"Could not find a lookup match for value {Math.Round(measurement2, 2).ToString("N2")}");
}
}
