Final answer:
True, exponential smoothing needs to be modified when a trend is present to accurately forecast future values using trend-adjusted methods.
Step-by-step explanation:
When a trend is present in data, exponential smoothing must indeed be modified to accurately forecast future values. Therefore, the statement is true. This is because standard exponential smoothing is designed to predict data assuming there is no trend or seasonality. However, when a trend is present, a variation of exponential smoothing called trend-adjusted exponential smoothing or Holt's linear trend method is used. This method takes into account both the recent level of the series and the recent trend, providing a way to forecast data that is trending upwards or downwards over time.