# C. ASCA

    # Start the HDANOVA R package
    library(HDANOVA)

# Analysis of Variance Simultaneous Component Analysis (ASCA)

The ANOVA part of ASCA includes all the possible variations of ANOVA demonstrated in the ANOVA section and more. Also, generalized linear models (GLM) can be used. The following theory will be exemplified:

- Basic ASCA
  - Permutation testing
  - Random effects
  - Scores and loadings
  - Data and confidence ellipsoids
  - Combined effects
  - Numeric effects
- ANOVA-PCA (APCA)
- PC-ANOVA
- MSCA
- LiMM-PCA

## HDANOVA

The ANOVA part of ASCA includes all the possible variations of ANOVA demonstrated in the ANOVA vignette and more. Also generalized linear models (GLM) can be used. We start by demonstrating HDANOVA with a fixed effect model of two factors with interactions.

    # Load Candy data
    data(candies)

    # Fit ASCA model
    mod <- hdanova(assessment ~ candy*assessor, data=candies)
    summary(mod)
    #> High-Dimensional Analysis of Variance fitted using 'lm' (Linear Model)
    #> - SS type II, sum coding, restricted model, least squares estimation
    #>                 Sum.Sq. Expl.var.(%)
    #> candy          33416.66        74.48
    #> assessor        1961.37         4.37
    #> candy:assessor  3445.73         7.68
    #> Residuals       6043.52        13.47

The summary shows that the candy effect is the largest by far.

## Basic ASCA

If we use the ASCA function directly, we get the same result as with HDANOVA, but in addition PCAs on the effect matrices are computed.

    # Fit ASCA model
    mod <- asca(assessment ~ candy*assessor, data=candies)
    summary(mod)
    #> Anova Simultaneous Component Analysis fitted using 'lm' (Linear Model)
    #> - SS type II, sum coding, restricted model, least squares estimation
    #>                 Sum.Sq. Expl.var.(%)
    #> candy          33416.66        74.48
    #> assessor        1961.37         4.37
    #> candy:assessor  3445.73         7.68
    #> Residuals       6043.52        13.47

This can also be done sequentially, expanding the model step by step.

    # Fit ASCA model step by step
    mod_hd <- hdanova(assessment ~ candy*assessor, data=candies)
    mod_asca <- sca(mod_hd)

### Permutation testing

To get more insight, we can perform permutation testing of the factors. Here we use approximate permutation.

    # Permutation testing (default = 1000 permutations, if not specified)
    mod <- asca(assessment ~ candy*assessor, data=candies, permute=TRUE)
    summary(mod)
    #> Anova Simultaneous Component Analysis fitted using 'lm' (Linear Model)
    #> - SS type II, sum coding, restricted model, least squares estimation, 1000 permutations
    #>                 Sum.Sq. Expl.var.(%) p-value
    #> candy          33416.66        74.48       0
    #> assessor        1961.37         4.37       0
    #> candy:assessor  3445.73         7.68       0
    #> Residuals       6043.52        13.47      NA

Here we see that all effects are significant, where the Candy effect is the dominating one. (The P-values are rounded from 0.001 to 0 in the print). This can also be visualised by looking at the sums-of-squares values obtained under permutation compared to the original value.

    permutationplot(mod, factor = "assessor")

Permutations can also be performed as a post processing of an ASCA object.

    mod <- asca(assessment ~ candy*assessor, data=candies)
    mod <- permutation(mod)

### Random effects

One can argue that the assessors are random effects, thus should be handled as such in the model. We can do this by adding r() around the assessor term. See also LiMM-PCA below for the REML estimation version.

    # Fit ASCA model with random assessor
    mod.mixed <- asca(assessment ~ candy*r(assessor), data=candies, permute=TRUE)
    summary(mod.mixed)
    #> Anova Simultaneous Component Analysis fitted using 'lmm' (Linear Mixed Model)
    #> - SS type II, sum coding, restricted model, least squares estimation, 1000 permutations
    #>                 Sum.Sq. Expl.var.(%) p-value
    #> candy          33416.66        74.48       0
    #> assessor        1961.37         4.37       0
    #> candy:assessor  3445.73         7.68       0
    #> Residuals       6043.52        13.47      NA

### Scores and loadings

The effects can be visualised through, e.g., loading and score plots to assess the relations between variables, objects and factors. If a factor is not specified, the first factor is plotted.

    par.old <- par(mfrow=c(2,1), mar=c(4,4,2,1))
    loadingplot(mod, scatter=TRUE, labels="names", main="Candy loadings")
    scoreplot(mod, main="Candy scores")

    par(par.old)

A specific factor can be plotted by specifying the factor name or number.

    par.old <- par(mfrow=c(2,1), mar=c(4,4,2,1))
    loadingplot(mod, factor="assessor", scatter=TRUE, labels="names", main="Assessor loadings")
    scoreplot(mod, factor="assessor", main="Assessor scores")

    par(par.old)

Score plots can be modified, e.g., omitting backprojections or adding spider plots.

    par.old <- par(mfrow=c(2,1), mar=c(4,4,2,1))
    scoreplot(mod, factor="assessor", main="Assessor scores", projections=FALSE)
    scoreplot(mod, factor="assessor", main="Assessor scores", spider=TRUE)

    par(par.old)

If the directions of the scores or loadings are not as expected, the signs can be flipped.

    mod <- signflip(mod, factor="candy", comp=1)
    par.old <- par(mfrow=c(2,1), mar=c(4,4,2,1))
    loadingplot(mod, scatter=TRUE, labels="names", main="Candy loadings")
    scoreplot(mod, main="Candy scores")

    par(par.old)

And scores and loadings can be extracted for further analysis.

    L <- loadings(mod, factor="candy")
    head(L)
    #>                 Comp 1        Comp 2      Comp 3      Comp 4
    #> transparent -0.3927649  0.0279168248 -0.30598369  0.77398098
    #> acid         0.1649285 -0.8042012208  0.47650301  0.24192158
    #> sweet        0.2235032  0.4607791525  0.52330000 -0.01751194
    #> raspberry    0.2277610  0.3663430297  0.35862959  0.50808527
    #> texture      0.4302019 -0.0004154248 -0.13000106  0.22107937
    #> strength    -0.3653312  0.0694885591  0.09828578 -0.09582978
    S <- scores(mod, factor="candy")
    head(S)
    #>     Comp 1   Comp 2     Comp 3    Comp 4
    #> 1 16.81343 4.844756 -0.2914198 0.1811588
    #> 2 16.81343 4.844756 -0.2914198 0.1811588
    #> 3 16.81343 4.844756 -0.2914198 0.1811588
    #> 4 16.81343 4.844756 -0.2914198 0.1811588
    #> 5 16.81343 4.844756 -0.2914198 0.1811588
    #> 6 16.81343 4.844756 -0.2914198 0.1811588

Finally, scores and loadings can be combined into a biplot.

    biplot(mod, factor="candy", labels="names")

### Data ellipsoids and confidence ellipsoids

To emphasize factor levels or assess factor level differences, we can add data ellipsoids or confidence ellipsoids to the score plot. The confidence ellipsoids are built on the assumption of balanced data, and their theories are built around crossed designs.

    par.old <- par(mfrow=c(2,1), mar=c(4,4,2,1))
    scoreplot(mod, ellipsoids="data", factor="candy", main="Data ellipsoids")
    scoreplot(mod, ellipsoids="confidence", factor="candy", main="Confidence ellipsoids")

    par(par.old)

If we repeat this for the mixed model, we see that both types of ellipsoids change together with the change in denominator term in the underlying ANOVA model. It should be noted that the theory for confidence ellipsoids in mixed models is not fully developed, so interpretation should be done with caution.

    par.old <- par(mfrow=c(2,1), mar=c(4,4,2,1))
    scoreplot(mod.mixed, ellipsoids="data", factor="candy", main="Data ellipsoids")
    scoreplot(mod.mixed, ellipsoids="confidence", factor="candy", main="Confidence ellipsoids")

    par(par.old)

### Combined effects

In some cases, it can be of interest to combine effects in ASCA. Here, we use an example with the Caldana data where we combine the light effect with the time:light interaction using the comb() function.

    # Load Caldana data
    data(caldana)

    # Combined effects
    mod.comb <- asca(compounds ~ time + comb(light + time:light), data=caldana)
    summary(mod.comb)
    #> Anova Simultaneous Component Analysis fitted using 'lm' (Linear Model)
    #> - SS type II, sum coding, restricted model, least squares estimation
    #>                  Sum.Sq. Expl.var.(%)
    #> time              154.58         9.69
    #> light+time:light  349.64        21.92
    #> Residuals        1091.14        68.39

When combined effects have a time factor, the scores can be plotted against time.

    # Scores plotted as a function of time
    par.old <- par(mfrow=c(2,1), mar = c(4,4,1,1))
    timeplot(mod.comb, factor="light", time="time", comb=2, comp=1, x_time=TRUE)
    timeplot(mod.comb, factor="light", time="time", comb=2, comp=2, x_time=TRUE)

    par(par.old)

### Quantitative effects

Quantitative effects, so-called covariates, can also be included in a model, though their use in ASCA are limited to ANOVA estimation and explained variance, not being used in subsequent PCA or permutation testing. We demonstrate this using the Caldana data again, but now recode the time effect to a quantitative effect, meaning it will be handled as a linear continuous effect.

    caldanaNum <- caldana
    caldanaNum$time <- as.numeric(as.character(caldanaNum$time))
    mod.num <- asca(compounds ~ time*light, data = caldanaNum)
    summary(mod.num)
    #> Anova Simultaneous Component Analysis fitted using 'lm' (Linear Model)
    #> - SS type II, sum coding, restricted model, least squares estimation
    #>            Sum.Sq. Expl.var.(%)
    #> time         55.42         3.47
    #> light       102.49         6.42
    #> time:light  109.56         6.87
    #> Residuals  1327.90        83.23

## ANOVA-PCA (APCA)

APCA differs from ASCA by adding the error term to the model before performing PCA instead of backprojecting errors afterwards.

    # Fit APCA model
    modp <- apca(assessment ~ candy*assessor, data=candies)
    summary(modp)
    #> Anova Principal Component Analysis fitted using 'lm' (Linear Model)
    #> - SS type II, sum coding, restricted model, least squares estimation
    #>                 Sum.Sq. Expl.var.(%)
    #> candy          33416.66        74.48
    #> assessor        1961.37         4.37
    #> candy:assessor  3445.73         7.68
    #> Residuals       6043.52        13.47

Plot scores and loadings.

    par.old <- par(mfrow=c(2,1), mar=c(4,4,2,1))
    loadingplot(modp, scatter=TRUE, labels="names", main="Candy loadings")
    scoreplot(modp, main="Candy scores")

    par(par.old)

## PC-ANOVA

In PC-ANOVA, a PCA is first applied to the data before the scores are subjected to ANOVA, effectively reversing the roles in ASCA. This means there will be one or more ANOVA tables in the summary of the output. In this example, we have chosen to use the number of components that explain at least 90% of the variation of the data.

    mod.pc <- pcanova(assessment ~ candy * assessor, data = candies, ncomp = 0.9)
    print(mod.pc)
    #> PC-ANOVA - Principal Components Analysis of Variance
    #>
    #> Call:
    #> pcanova(formula = assessment ~ candy * assessor, data = candies,     ncomp = 0.9)
    summary(mod.pc)
    #> PC-ANOVA - Principal Components Analysis of Variance
    #>
    #> Call:
    #> pcanova(formula = assessment ~ candy * assessor, data = candies,     ncomp = 0.9)
    #> $`Comp. 1`
    #> Anova Table (Type II tests)
    #>
    #> Response: assessment
    #>                 Sum Sq  Df  F value  Pr(>F)
    #> candy          31470.6   4 780.1762 < 2e-16 ***
    #> assessor         224.9  10   2.2304 0.02089 *
    #> candy:assessor   707.7  40   1.7545 0.01158 *
    #> Residuals       1109.3 110
    #> ---
    #> Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
    #>
    #> $`Comp. 2`
    #> Anova Table (Type II tests)
    #>
    #> Response: assessment
    #>                Sum Sq  Df F value    Pr(>F)
    #> candy          1573.8   4 33.1604 < 2.2e-16 ***
    #> assessor        278.3  10  2.3455 0.0150274 *
    #> candy:assessor 1053.3  40  2.2193 0.0005888 ***
    #> Residuals      1305.2 110
    #> ---
    #> Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
    #>
    #> $`Comp. 3`
    #> Anova Table (Type II tests)
    #>
    #> Response: assessment
    #>                 Sum Sq  Df F value    Pr(>F)
    #> candy           307.12   4   7.646 1.790e-05 ***
    #> assessor       1006.62  10  10.024 8.574e-12 ***
    #> candy:assessor  484.02  40   1.205    0.2229
    #> Residuals      1104.61 110
    #> ---
    #> Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

When creating score and loading plots for PC-ANOVA, the ‘global’ scores and loadings will be shown, but the factors can still be used for manipulating the symbols.

    par.old <- par(mfrow=c(2,1), mar=c(4,4,2,1))
    loadingplot(mod.pc, scatter=TRUE, labels="names", main="Global loadings")
    scoreplot(mod.pc, main="Global scores")

    par(par.old)

## MSCA

Multilevel Simultaneous Component Analysis (MSCA) is a version of ASCA that assumes a single factor to be used as a between-individuals factor, while the the within-individuals is assumed implicitly.

    # Default MSCA model with a single factor
    mod.msca <- msca(assessment ~ candy, data=candies)
    summary(mod.msca)
    #> Multilevel Simultaneous Component Analysis fitted using 'lm' (Linear Model)
    #> - SS type II, sum coding, restricted model, least squares estimation
    #>          Sum.Sq. Expl.var.(%)
    #> Between 33416.66        74.48
    #> Within  11450.62        25.52

Scoreplots can be created for the between-individuals factor and the within-individuals factor, and for each level of the within-individuals factor.

    # Scoreplot for between-individuals factor
    scoreplot(mod.msca)

    # Scoreplot of within-individuals factor
    scoreplot(mod.msca, factor="within")

    # .. per factor level
    par.old <- par(mfrow=c(3,2), mar=c(4,4,2,1), mgp=c(2,0.7,0))
    for(i in 1:length(mod.msca$scores.within))
     scoreplot(mod.msca, factor="within", within_level=i,
               main=paste0("Level: ", names(mod.msca$scores.within)[i]),
               panel.first=abline(v=0,h=0,col="gray",lty=2))
    par(par.old)

## LiMM-PCA

A version of LiMM-PCA is also implemented in HDANOVA. It combines REML-estimated mixed models with PCA and scales the back-projected errors according to degrees of freedom or effective dimensions (user choice).

    # Default LiMM-PCA model with two factors and interaction, 8 PCA components
    mod.reml <- limmpca(assessment ~ candy*r(assessor), data=candies, pca.in=8)
    summary(mod.reml)
    #> LiMM-PCA fitted using 'lmm' (Linear Mixed Model)
    #> - SS type III, sum coding, restricted model, REML estimation
    #>                 Sum.Sq. Expl.var.(%)
    #> candy          33415.98        74.73
    #> candy:assessor  1335.70         2.99
    #> assessor        1101.43         2.46
    #> Residuals       8865.22        19.82
    scoreplot(mod.reml, factor="candy")

One can also use least squares estimation without REML. This affects the random effects and scaling of backprojections.

    # LiMM-PCA with least squares estimation and 8 PCA components
    mod.ls <- limmpca(assessment ~ candy*r(assessor), data=candies, REML=NULL, pca.in=8)
    summary(mod.ls)
    #> LiMM-PCA fitted using 'lmm' (Linear Mixed Model)
    #> - SS type III, sum coding, restricted model, least squares estimation
    #>                 Sum.Sq. Expl.var.(%)
    #> candy          33415.98        74.73
    #> assessor        1948.75         4.36
    #> candy:assessor  3419.04         7.65
    #> Residuals       5934.46        13.27
    scoreplot(mod.ls)

## Repeated measures

We revisit the simulated data from the ANOVA vignette to demonstrate ASCA with repeated measures. The data are subset, a time effect is added, and the response is extended to the multivariate case.

    set.seed(123)
    # Original simulation
    dat <- data.frame(
      feed  = factor(rep(rep(c("low","high"), each=6), 4)),
      breed = factor(rep(c("NRF","Hereford","Angus"), 16)),
      bull  = factor(rep(LETTERS[1:4], each = 12)),
      daughter = factor(c(rep(letters[1:4], 3), rep(letters[5:8], 3), rep(letters[9:12], 3), rep(letters[13:16], 3))),
      age   = round(rnorm(48, mean = 36, sd = 5))
    )
    dat$yield <- 150*with(dat, 10 + 3 * as.numeric(feed) + as.numeric(breed) +
                            2 * as.numeric(bull) + 1 * as.numeric(sample(dat$daughter, 48)) +
                            0.5 * age + rnorm(48, sd = 2))
    # Extended to repeated measures
    long <- dat[c(1:4,9:12), c("feed", "daughter", "yield")]
    long <- rbind(long, long, long)
    long$daughter <- factor(long$daughter) # Remove redundant daughters
    long$time  <- factor(rep(1:3, each=8))
    long$yield <- long$yield + rnorm(24, sd = 100) + rep(c(-200,0,200), each=8)
    # Made multiresponse (no added structure, only noise)
    long$yield <- I(matrix(rep(long$yield,10),nrow=length(long$yield),ncol=10)) + rnorm(length(long$yield)*10)

Analysing the data with ASCA using the least squares approach.

    # Least squares mixed model ASCA
    mod.rm.asca <- asca(yield ~ r(daughter) + feed*r(time), data = long)
    summary(mod.rm.asca)
    #> Anova Simultaneous Component Analysis fitted using 'lmm' (Linear Mixed Model)
    #> - SS type II, sum coding, restricted model, least squares estimation
    #>                Sum.Sq. Expl.var.(%)
    #> daughter   31997318.91        23.01
    #> feed         306570.25         0.22
    #> time        4309830.00         3.10
    #> feed:time     57834.68         0.04
    #> Residuals 102393907.07        73.63

Corresponding analysis using the LiMM-PCA approach with REML estimation.

    # REML mixed model LiMM-PCA
    mod.rm.limmpca <- limmpca(yield ~ r(daughter) + feed*r(time), data = long, pca.in=10)
    #> boundary (singular) fit: see help('isSingular')
    #> boundary (singular) fit: see help('isSingular')
    summary(mod.rm.limmpca)
    #> LiMM-PCA fitted using 'lmm' (Linear Mixed Model)
    #> - SS type III, sum coding, restricted model, REML estimation
    #>                Sum.Sq. Expl.var.(%)
    #> feed         306570.25         0.22
    #> feed:time         0.51         0.00
    #> daughter   10645045.16         7.65
    #> time              0.09         0.00
    #> Residuals 128113850.32        92.12