# BookRiff

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## What is the dependent variable in survival analysis?

Dependent variable or response is the waiting time until the occurrence of an event. 2. Observations are censored, in the sense that for some units the event of interest has not occurred at the time the data are ana- lyzed.

## Is hazard ratio time-dependent?

The hazard ratio is given by HR(t) = hx+1(t)/hx(t) = exp[β + γ. x.f(t)] for a unit increase in the variable X, and is time-dependent through the function f(t). If γ > 0 (γ < 0), then the HR increases (decreases) over time.

## Is survival time a continuous variable?

The effect on survival time of age at operation, a continuous variable, should also be examined. Cox regression (8) can be used in both cases.

## What is time-dependent hazard?

The Cox proportional-hazards regression model for time-to-event data may be used with covariates, independent variables, or predictor variables that vary over time. These are called time-dependent covariates. Their use is much more complicated in practice than the fixed (time-independent) covariates.

## What is Cox regression used for?

Cox regression (or proportional hazards regression) is method for investigating the effect of several variables upon the time a specified event takes to happen. In the context of an outcome such as death this is known as Cox regression for survival analysis.

## Is Kaplan-Meier a logistic regression?

We discuss the use of standard logistic regression techniques to estimate hazard rates and survival curves from censored data. In fact, the logistic regression estimates are closely related to Kaplan-Meier curves, and approach the Kaplan-Meier estimate as the number of parameters grows large.

## What is time-dependent analysis?

Basically, in a time-dependent analysis, the follow-up time for each patient is divided into different time windows. First, for each time –window, a separate Cox analysis is carried out using the specific value of the time-dependent variable at the beginning of that specific time window (Figure 3).

## What is survival time in survival analysis?

Survival Time is defined as the time starting from a predefined point to the occurrence of the event of interest[5]. The Kaplan-Meier Survival Curve is the probability of surviving in a given length of time where time is considered in small intervals.

## What is time dependent?

Filters. (mathematics, physics) Determined by the value of a variable representing time.

## How is the analysis of time dependent effects done?

The proper analysis of effects over time should be driven by a clear research question. Both kinds of research questions, that is those of time-dependent effects as well those of time-dependent risk factors, can be analyzed with time-dependent Cox regression analysis.

## When to use time dependent Cox regression analysis?

Both kinds of research questions, that is those of time-dependent effects as well those of time-dependent risk factors, can be analyzed with time-dependent Cox regression analysis. It will be shown that using time-dependent risk factors usually implies focusing on short-term effects only.

## Can a time dependent covariate be a confounder?

With time-dependent covariates, however, there is an even greater risk that a covariate during follow-up is (partly) a result of the risk factor we study. In other words, a time-dependent covariate could be a confounder, but could also be an intermediate in the causal pathway.

## Which is an example of a time dependent covariate?

Time-dependent covariates are those that may change in value for a given subject over the course of observation. In contrast, time-independent covariates are those whose value remains constant over time. Take Stanford heart transplant study as example, regarding covariate TRANS (which is equal to 1 if the patient has already had a